WO2018022779A1

WO2018022779A1 - Evacuating blades in a storage array that includes a plurality of blades

Info

Publication number: WO2018022779A1
Application number: PCT/US2017/043993
Authority: WO
Inventors: John D. Davis; Roland Dreier; Warren W. JEW; Andrew KLEINERMAN; Taher Vohra; Xiaohui Wang
Original assignee: Pure Storage, Inc.
Priority date: 2016-07-26
Filing date: 2017-07-26
Publication date: 2018-02-01

Abstract

Evacuating blades in a storage array that includes a plurality of blades, including: detecting an occurrence of a blade evacuation event associated with one or more blades; iteratively until migration has completed for each of the blades associated with the blade evacuation event: selecting, in dependence upon a blade redundancy policy, one or more next blades to be evacuated from the storage array; migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the next blade; and migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades.

Description

EVACUATING BLADES IN A STORAGE ARRAY THAT INCLUDES

A PLURALITY OF BLADES

BACKGROUND

[0001] Solid-state memory, such as flash, is currently in use in solid-state drives (SSD) to augment or replace conventional hard disk drives (HDD), writable CD (compact disk) or writable DVD (digital versatile disk) drives, collectively known as spinning media, and tape drives, for storage of large amounts of data. Flash and other solid-state memories have characteristics that differ from spinning media. Yet, many solid-state drives are designed to conform to hard disk drive standards for compatibility reasons, which makes it difficult to provide enhanced features or take advantage of unique aspects of flash and other solid-state memory. One aspect of the embodiments described below is the ability to conveniently upgrade the storage system components.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Figure 1A illustrates a first example system for data storage in accordance with some implementations.

[0003] Figure IB illustrates a second example system for data storage in accordance with some implementations.

[0004] Figure 1C illustrates a third example system for data storage in accordance with some implementations.

[0005] Figure ID illustrates a fourth example system for data storage in accordance with some implementations.

[0006] Fig. 2A is a perspective view of a storage cluster with multiple storage nodes and internal storage coupled to each storage node to provide network attached storage, in accordance with some embodiments.

[0007] Fig. 2B is a block diagram showing an interconnect switch coupling multiple storage nodes in accordance with some embodiments.

[0008] Fig. 2C is a multiple level block diagram, showing contents of a storage node and contents of one of the non-volatile solid state storage units in accordance with some embodiments.

[0009] Fig. 2D shows a storage server environment, which uses embodiments of the storage nodes and storage units of Figs. 1-3 in accordance with some embodiments. [0010] Fig. 2E is a blade hardware block diagram, showing a control plane, compute and storage planes, and authorities interacting with underlying physical resources, in accordance with some embodiments.

[0011] Fig. 2F depicts elasticity software layers in blades of a storage cluster, in accordance with some embodiments.

[0012] Fig. 2G depicts authorities and storage resources in blades of a storage cluster, in accordance with some embodiments.

[0013] Figure 3A sets forth a diagram of a storage system that is coupled for data communications with a cloud services provider in accordance with some embodiments of the present disclosure.

[0014] Figure 3B sets forth a diagram of a storage system in accordance with some embodiments of the present disclosure.

[0015] Figure 4 sets forth a block diagram of a storage system configured for evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0016] Figure 5 sets forth a diagram of a set of blades useful in evacuating blades in a storage array according to embodiments of the present disclosure.

[0017] Figure 6 sets forth a diagram of a blade useful in evacuating blades in a storage array according to embodiments of the present disclosure.

[0018] Figure 7 sets forth a flow chart illustrating an example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0019] Figure 8 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0020] Figure 9 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0021] Figure 10 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0022] Figure 11 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure. [0023] Figure 12 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0024] Figure 13 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

[0025] Figure 14 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure.

DESCRIPTION OF EMBODIMENTS

[0026] Embodiments of the present disclosure relate to evacuating blades in a storage array that includes a plurality of blades. The storage arrays may provide persistent data storage through the use of one or more blades that may include compute resources (e.g., computer processors), storage resources (e.g., solid-state drives (' SSDs'), or any combination thereof. As the components of such blades age, the blades may not perform as well as they did when initially deployed. Furthermore, because technology is constantly advancing, as the blades age more efficient technologies may become available. As such, it may desirable to replace aging blades with new blades.

[0027] Embodiments of the present disclosure may be useful in evacuating blades in a storage array that includes a plurality of blades by detecting an occurrence of a blade evacuation event associated with one or more blades. The blade evacuation event may indicate that the one or more blades should no longer be written to as the blades have been targeted for removal from the storage array. Readers will appreciate that one or more blades may be targeted for removal from the storage array for a variety of reasons. For example, the blades may utilize relatively old memory devices that have a smaller storage capacity than relatively new memory devices that may be available as replacements for the relatively old memory devices. Alternatively, the blades may utilize relatively old memory devices that have higher access latencies and can't perform as many IOPS as relatively new memory devices that may be available as replacements for the relatively old memory devices. For example, the blades may include DDR3 DRAM memory devices that can be replaced with DDR4 DRAM memory devices that operate at higher frequencies, lower power consumption levels, and so on. The one or more blades may therefore be targeted for removal from the storage array as part of an upgrade to the storage array. Readers will appreciate that the one or more blades may be targeted for removal from the storage array for other reasons, and readers will further appreciate that the one or more blades may be targeted for removal from the storage array in spite of the fact that the blades may still be properly functioning with no indication that a failure of the blades is imminent. Example embodiments of the present disclosure are further described with reference to the accompanying drawings, beginning with Figure 1A.

[0028] Figure 1A illustrates an example system for data storage, in accordance with some implementations. System 100 (also referred to as "storage system" herein) includes numerous elements for purposes of illustration rather than limitation. It may be noted that system 100 may include the same, more, or fewer elements configured in the same or different manner in other implementations.

[0029] System 100 includes a number of computing devices 164. Computing devices (also referred to as "client devices" herein) may be for example, a server in a data center, a workstation, a personal computer, a notebook, or the like. Computing devices 164 are coupled for data communications to one or more storage arrays 102 through a storage area network (SAN) 158 or a local area network (LAN) 160.

[0030] The SAN 158 may be implemented with a variety of data communications fabrics, devices, and protocols. For example, the fabrics for SAN 158 may include Fibre Channel, Ethernet, Infiniband, Serial Attached Small Computer System Interface (SAS), or the like. Data communications protocols for use with SAN 158 may include Advanced Technology Attachment (ATA), Fibre Channel Protocol, Small Computer System Interface (SCSI), Internet Small Computer System Interface (iSCSI), HyperSCSI, Non-Volatile Memory Express (NVMe) over Fabrics, or the like. It may be noted that SAN 158 is provided for illustration, rather than limitation. Other data communication couplings may be implemented between computing devices 164 and storage arrays 102.

[0031] The LAN 160 may also be implemented with a variety of fabrics, devices, and protocols. For example, the fabrics for LAN 160 may include Ethernet (802.3), wireless (802.1 1), or the like. Data communication protocols for use in LAN 160 may include Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Internet Protocol (IP), HyperText Transfer Protocol (HTTP), Wireless Access Protocol (WAP), Handheld Device Transport Protocol (HDTP), Session Initiation Protocol (SIP), Real Time Protocol (RTP), or the like.

[0032] Storage arrays 102 may provide persistent data storage for the computing devices 164. Storage array 102A may be contained in a chassis (not shown), and storage array 102B may be contained in another chassis (not shown), in implementations. Storage array 102A and 102B may include one or more storage array controllers 110 (also referred to as "controller" herein). A storage array controller 110 may be embodied as a module of automated computing machinery comprising computer hardware, computer software, or a combination of computer hardware and software. In some implementations, the storage array controllers 110 may be configured to carry out various storage tasks. Storage tasks may include writing data received from the computing devices 164 to storage array 102, erasing data from storage array 102, retrieving data from storage array 102 and providing data to computing devices 164, monitoring and reporting of disk utilization and performance, performing redundancy operations, such as Redundant Array of Independent Drives (RAID) or RAID-like data redundancy operations, compressing data, encrypting data, and so forth.

[0033] Storage array controller 110 may be implemented in a variety of ways, including as a Field Programmable Gate Array (FPGA), a Programmable Logic Chip (PLC), an Application Specific Integrated Circuit (ASIC), System-on-Chip (SOC), or any computing device that includes discrete components such as a processing device, central processing unit, computer memory, or various adapters. Storage array controller 110 may include, for example, a data communications adapter configured to support communications via the SAN 158 or LAN 160. In some implementations, storage array controller 110 may be independently coupled to the LAN 160. In implementations, storage array controller 110 may include an I/O controller or the like that couples the storage array controller 110 for data communications, through a midplane (not shown), to a persistent storage resource 170 (also referred to as a "storage resource" herein). The persistent storage resource 170 main include any number of storage drives 171 (also referred to as "storage devices" herein) and any number of non-volatile Random Access Memory (NVRAM) devices (not shown).

[0034] In some implementations, the NVRAM devices of a persistent storage resource 170 may be configured to receive, from the storage array controller 110, data to be stored in the storage drives 171. In some examples, the data may originate from computing devices 164. In some examples, writing data to the NVRAM device may be carried out more quickly than directly writing data to the storage drive 171. In implementations, the storage array controller 110 may be configured to utilize the NVRAM devices as a quickly accessible buffer for data destined to be written to the storage drives 171. Latency for write requests using NVRAM devices as a buffer may be improved relative to a system in which a storage array controller 110 writes data directly to the storage drives 171. In some implementations, the NVRAM devices may be implemented with computer memory in the form of high bandwidth, low latency RAM. The NVRAM device is referred to as "non-volatile" because the NVRAM device may receive or include a unique power source that maintains the state of the RAM after main power loss to the NVRAM device. Such a power source may be a battery, one or more capacitors, or the like. In response to a power loss, the NVRAM device may be configured to write the contents of the RAM to a persistent storage, such as the storage drives 171.

[0035] In implementations, storage drive 171 may refer to any device configured to record data persistently, where "persistently" or "persistent" refers as to a device's ability to maintain recorded data after loss of power. In some implementations, storage drive 171 may correspond to non-disk storage media. For example, the storage drive 171 may be one or more solid-state drives (SSDs), flash memory based storage, any type of solid-state nonvolatile memory, or any other type of non-mechanical storage device. In other

implementations, storage drive 171 may include may include mechanical or spinning hard disk, such as hard-disk drives (HDD).

[0036] In some implementations, the storage array controllers 110 may be configured for offloading device management responsibilities from storage drive 171 in storage array 102. For example, storage array controllers 110 may manage control information that may describe the state of one or more memory blocks in the storage drives 171. The control information may indicate, for example, that a particular memory block has failed and should no longer be written to, that a particular memory block contains boot code for a storage array controller 110, the number of program -erase (P/E) cycles that have been performed on a particular memory block, the age of data stored in a particular memory block, the type of data that is stored in a particular memory block, and so forth. In some implementations, the control information may be stored with an associated memory block as metadata. In other implementations, the control information for the storage drives 171 may be stored in one or more particular memory blocks of the storage drives 171 that are selected by the storage array controller 110. The selected memory blocks may be tagged with an identifier indicating that the selected memory block contains control information. The identifier may be utilized by the storage array controllers 110 in conjunction with storage drives 171 to quickly identify the memory blocks that contain control information. For example, the storage controllers 110 may issue a command to locate memory blocks that contain control information. It may be noted that control information may be so large that parts of the control information may be stored in multiple locations, that the control information may be stored in multiple locations for purposes of redundancy, for example, or that the control information may otherwise be distributed across multiple memory blocks in the storage drive 171. [0037] In implementations, storage array controllers 1 10 may offload device management responsibilities from storage drives 171 of storage array 102 by retrieving, from the storage drives 171, control information describing the state of one or more memory blocks in the storage drives 171. Retrieving the control information from the storage drives 171 may be carried out, for example, by the storage array controller 1 10 querying the storage drives 171 for the location of control information for a particular storage drive 171. The storage drives 171 may be configured to execute instructions that enable the storage drive 171 to identify the location of the control information. The instructions may be executed by a controller (not shown) associated with or otherwise located on the storage drive 171 and may cause the storage drive 171 to scan a portion of each memory block to identify the memory blocks that store control information for the storage drives 171. The storage drives 171 may respond by sending a response message to the storage array controller 1 10 that includes the location of control information for the storage drive 171. Responsive to receiving the response message, storage array controllers 110 may issue a request to read data stored at the address associated with the location of control information for the storage drives 171.

[0038] In other implementations, the storage array controllers 110 may further offload device management responsibilities from storage drives 171 by performing, in response to receiving the control information, a storage drive management operation. A storage drive management operation may include, for example, an operation that is typically performed by the storage drive 171 (e.g., the controller (not shown) associated with a particular storage drive 171). A storage drive management operation may include, for example, ensuring that data is not written to failed memory blocks within the storage drive 171, ensuring that data is written to memory blocks within the storage drive 171 in such a way that adequate wear leveling is achieved, and so forth.

[0039] In implementations, storage array 102 may implement two or more storage array controllers 1 10. For example, storage array 102A may include storage array controllers 1 10A and storage array controllers 1 10B. At a given instance, a single storage array controller 1 10 (e.g., storage array controller 1 10A) of a storage system 100 may be designated with primary status (also referred to as "primary controller" herein), and other storage array controllers 1 10 (e.g., storage array controller 1 10A) may be designated with secondary status (also referred to as "secondary controller" herein). The primary controller may have particular rights, such as permission to alter data in persistent storage resource 170 (e.g., writing data to persistent storage resource 170). At least some of the rights of the primary controller may supersede the rights of the secondary controller. For instance, the secondary controller may not have permission to alter data in persistent storage resource 170 when the primary controller has the right. The status of storage array controllers 110 may change. For example, storage array controller 110A may be designated with secondary status, and storage array controller 110B may be designated with primary status.

[0040] In some implementations, a primary controller, such as storage array controller 110A, may serve as the primary controller for one or more storage arrays 102, and a second controller, such as storage array controller 110B, may serve as the secondary controller for the one or more storage arrays 102. For example, storage array controller 110A may be the primary controller for storage array 102A and storage array 102B, and storage array controller HOB may be the secondary controller for storage array 102A and 102B. In some implementations, storage array controllers 1 IOC and HOD (also referred to as "storage processing modules") may neither have primary or secondary status. Storage array controllers 1 IOC and 110D, implemented as storage processing modules, may act as a communication interface between the primary and secondary controllers (e.g., storage array controllers 110A and 110B, respectively) and storage array 102B. For example, storage array controller 110A of storage array 102A may send a write request, via SAN 158, to storage array 102B. The write request may be received by both storage array controllers 1 IOC and 110D of storage array 102B. Storage array controllers HOC and HOD facilitate the communication, e.g., send the write request to the appropriate storage drive 171. It may be noted that in some implementations storage processing modules may be used to increase the number of storage drives controlled by the primary and secondary controllers.

[0041] In implementations, storage array controllers 110 are communicatively coupled, via a midplane (not shown), to one or more storage drives 171 and to one or more NVRAM devices (not shown) that are included as part of a storage array 102. The storage array controllers 110 may be coupled to the midplane via one or more data communication links and the midplane may be coupled to the storage drives 171 and the NVRAM devices via one or more data communications links. The data communications links described herein are collectively illustrated by data communications links 108 and may include a Peripheral Component Interconnect Express (PCIe) bus, for example.

[0042] Figure IB illustrates an example system for data storage, in accordance with some implementations. Storage array controller 101 illustrated in Figure IB may similar to the storage array controllers 110 described with respect to Figure 1A. In one example, storage array controller 101 may be similar to storage array controller 11 OA or storage array controller HOB. Storage array controller 101 includes numerous elements for purposes of illustration rather than limitation. It may be noted that storage array controller 101 may include the same, more, or fewer elements configured in the same or different manner in other implementations. It may be noted that elements of Figure 1 A may be included below to help illustrate features of storage array controller 101.

[0043] Storage array controller 101 may include one or more processing devices 104 and random access memory (RAM) 1 1 1. Processing device 104 (or controller 101) represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processing device 104 (or controller 101) may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VUW) microprocessor, or a processor implementing other instruction sets or processors implementing a combination of instruction sets. The processing device 104 (or controller 101) may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like.

[0044] The processing device 104 may be connected to the RAM 1 1 1 via a data

communications link 106, which may be embodied as a high speed memory bus such as a Double-Data Rate 4 (DDR4) bus. Stored in RAM 1 11 is an operating system 112. In some implementations, instructions 1 13 are stored in RAM 1 1 1. Instructions 1 13 may include computer program instructions for performing operations in in a direct-mapped flash storage system. In one embodiment, a direct-mapped flash storage system is one that that addresses data blocks within flash drives directly and without an address translation performed by the storage controllers of the flash drives.

[0045] In implementations, storage array controller 101 includes one or more host bus adapters 103 that are coupled to the processing device 104 via a data communications link 105. In implementations, host bus adapters 103 may be computer hardware that connects a host system (e.g., the storage array controller) to other network and storage arrays. In some examples, host bus adapters 103 may be a Fibre Channel adapter that enables the storage array controller 101 to connect to a SAN, an Ethernet adapter that enables the storage array controller 101 to connect to a LAN, or the like. Host bus adapters 103 may be coupled to the processing device 104 via a data communications link 105 such as, for example, a PCIe bus.

[0046] In implementations, storage array controller 101 may include a host bus adapter 1 14 that is coupled to an expander 1 15. The expander 1 15 may be used to attach a host system to a larger number of storage drives. The expander 1 15 may, for example, be a SAS expander utilized to enable the host bus adapter 114 to attach to storage drives in an implementation where the host bus adapter 114 is embodied as a SAS controller.

[0047] In implementations, storage array controller 101 may include a switch 116 coupled to the processing device 104 via a data communications link 109. The switch 116 may be a computer hardware device that can create multiple endpoints out of a single endpoint, thereby enabling multiple devices to share a single endpoint. The switch 116 may, for example, be a PCIe switch that is coupled to a PCIe bus (e.g., data communications link 109) and presents multiple PCIe connection points to the midplane.

[0048] In implementations, storage array controller 101 includes a data communications link 107 for coupling the storage array controller 101 to other storage array controllers. In some examples, data communications link 107 may be a QuickPath Interconnect (QPI) interconnect.

[0049] A traditional storage system that uses traditional flash drives may implement a process across the flash drives that are part of the traditional storage system. For example, a higher level process of the storage system may initiate and control a process across the flash drives. However, a flash drive of the traditional storage system may include its own storage controller that also performs the process. Thus, for the traditional storage system, a higher level process (e.g., initiated by the storage system) and a lower level process (e.g., initiated by a storage controller of the storage system) may both be performed.

[0050] To resolve various deficiencies of a traditional storage system, operations may be performed by higher level processes and not by the lower level processes. For example, the flash storage system may include flash drives that do not include storage controllers that provide the process. Thus, the operating system of the flash storage system itself may initiate and control the process. This may be accomplished by a direct-mapped flash storage system that addresses data blocks within the flash drives directly and without an address translation performed by the storage controllers of the flash drives.

[0051] The operating system of the flash storage system may identify and maintain a list of allocation units across multiple flash drives of the flash storage system. The allocation units may be entire erase blocks or multiple erase blocks. The operating system may maintain a map or address range that directly maps addresses to erase blocks of the flash drives of the flash storage system.

[0052] Direct mapping to the erase blocks of the flash drives may be used to rewrite data and erase data. For example, the operations may be performed on one or more allocation units that include a first data and a second data where the first data is to be retained and the second data is no longer being used by the flash storage system. The operating system may initiate the process to write the first data to new locations within other allocation units and erasing the second data and marking the allocation units as being available for use for subsequent data. Thus, the process may only be performed by the higher level operating system of the flash storage system without an additional lower level process being performed by controllers of the flash drives.

[0053] Advantages of the process being performed only by the operating system of the flash storage system include increased reliability of the flash drives of the flash storage system as unnecessary or redundant write operations are not being performed during the process. One possible point of novelty here is the concept of initiating and controlling the process at the operating system of the flash storage system. In addition, the process can be controlled by the operating system across multiple flash drives. This is contrast to the process being performed by a storage controller of a flash drive.

[0054] A storage system can consist of two storage array controllers that share a set of drives for failover purposes, or it could consist of a single storage array controller that provides a storage service that utilizes multiple drives, or it could consist of a distributed network of storage array controllers each with some number of drives or some amount of Flash storage where the storage array controllers in the network collaborate to provide a complete storage service and collaborate on various aspects of a storage service including storage allocation and garbage collection.

[0055] Figure 1C illustrates a third example system 117 for data storage in accordance with some implementations. System 117 (also referred to as "storage system" herein) includes numerous elements for purposes of illustration rather than limitation. It may be noted that system 117 may include the same, more, or fewer elements configured in the same or different manner in other implementations.

[0056] In one embodiment, system 117 includes a dual Peripheral Component Interconnect (PCI) flash storage device 118 with separately addressable fast write storage. System 117 may include a storage controller 119. In one embodiment, storage controller 119 may be a CPU, ASIC, FPGA, or any other circuitry that may implement control structures necessary according to the present disclosure. In one embodiment, system 117 includes flash memory devices (e.g., including flash memory devices 120a-n), operatively coupled to various channels of the storage device controller 119. Flash memory devices 120a-n, may be presented to the controller 119 as an addressable collection of Flash pages, erase blocks, and/or control elements sufficient to allow the storage device controller 119 to program and retrieve various aspects of the Flash. In one embodiment, storage device controller 119 may perform operations on flash memory devices 120A-N including storing and retrieving data content of pages, arranging and erasing any blocks, tracking statistics related to the use and reuse of Flash memory pages, erase blocks, and cells, tracking and predicting error codes and faults within the Flash memory, controlling voltage levels associated with programming and retrieving contents of Flash cells, etc.

[0057] In one embodiment, system 117 may include random access memory (RAM) 121 to store separately addressable fast-write data. In one embodiment, RAM 121 may be one or more separate discrete devices. In another embodiment, RAM 121 may be integrated into storage device controller 119 or multiple storage device controllers. The RAM 121 may be utilized for other purposes as well, such as temporary program memory for a processing device (E.g., a central processing unit (CPU)) in the storage device controller 119.

[0058] In one embodiment, system 119 may include a stored energy device 122, such as a rechargeable battery or a capacitor. Stored energy device 122 may store energy sufficient to power the storage device controller 119, some amount of the RAM (e.g., RAM 121), and some amount of Flash memory (e.g., Flash memory 120a-120n) for sufficient time to write the contents of RAM to Flash memory. In one embodiment, storage device controller 119 may write the contents of RAM to Flash Memory if the storage device controller detects loss of external power.

[0059] In one embodiment, system 117 includes two data communications links 123a, 123b. In one embodiment, data communications links 123a, 123b may be PCI interfaces. In another embodiment, data communications links 123a, 123b may be based on other communications standards (e.g., HyperTransport, InfiBand, etc.). Data communications links 123a, 123b may be based on non-volatile memory express (NVMe) or NCMe over fabrics (NVMf) specifications that allow external connection to the storage device controller 119 from other components in the storage system 117. It should be noted that data communications links may be interchangeably referred to herein as PCI buses for convenience.

[0060] System 117 may also include an external power source (not shown), which may be provided over one or both data communications links 123a, 123b, or which may be provided separately. An alternative embodiment includes a separate Flash memory (not shown) dedicated for use in storing the content of RAM 121. The storage device controller 119 may present a logical device over a PCI bus which may include an addressable fast-write logical device, or a distinct part of the logical address space of the storage device 118, which may be presented as PCI memory or as persistent storage. In one embodiment, operations to store into the device are directed into the RAM 121. On power failure, the storage device controller 1 19 may write stored content associated with the addressable fast-write logical storage to Flash memory (e.g., Flash memory 120a-n) for long-term persistent storage.

[0061] In one embodiment, the logical device may include some presentation of some or all of the content of the Flash memory devices 120a-n, where that presentation allows a storage system including a storage device 1 18 (e.g., storage system 1 17) to directly address Flash memory pages and directly reprogram erase blocks from storage system components that are external to the storage device through the PCI bus. The presentation may also allow one or more of the external components to control and retrieve other aspects of the Flash memory including some or all of: tracking statistics related to use and reuse of Flash memory pages, erase blocks, and cells across all the Flash memory devices; tracking and predicting error codes and faults within and across the Flash memory devices; controlling voltage levels associated with programming and retrieving contents of Flash cells; etc.

[0062] In one embodiment, the stored energy device 122 may be sufficient to ensure completion of in-progress operations to the Flash memory devices 107a-120n stored energy device 122 may power storage device controller 1 19 and associated Flash memory devices (e.g., 120a-n) for those operations, as well as for the storing of fast-write RAM to Flash memory. Stored energy device 122 may be used to store accumulated statistics and other parameters kept and tracked by the Flash memory devices 120a-n and/or the storage device controller 1 19. Separate capacitors or stored energy devices (such as smaller capacitors near or embedded within the Flash memory devices themselves) may be used for some or all of the operations described herein.

[0063] Various schemes may be used to track and optimize the life span of the stored energy component, such as adjusting voltage levels over time, partially discharging the storage energy device 122 to measure corresponding discharge characteristics, etc. If the available energy decreases over time, the effective available capacity of the addressable fast-write storage may be decreased to ensure that it can be written safely based on the currently available stored energy.

[0064] Figure ID illustrates a third example system 124 for data storage in accordance with some implementations. In one embodiment, system 124 includes storage controllers 125a, 125b. In one embodiment, storage controllers 125a, 125b are operative ly coupled to Dual PCI storage devices 1 19a, 1 19b and 1 19c, 1 19d, respectively. Storage controllers 125a, 125b may be operatively coupled (e.g., via a storage network 130) to some number of host computers 127a-n. [0065] In one embodiment, two storage controllers (e.g., 125a and 125b) provide storage services, such as a small computer system interface (SCSI) block storage array, a file server, an object server, a database or data analytics service, etc. The storage controllers 125a, 125b may provide services through some number of network interfaces (e.g., 126a-d) to host computers 127a-n outside of the storage system 124. Storage controllers 125a, 125b may provide integrated services or an application entirely within the storage system 124, forming a converged storage and compute system. The storage controllers 125a, 125b may utilize the fast write memory within or across storage devicesl 19a-d to journal in progress operations to ensure the operations are not lost on a power failure, storage controller removal, storage controller or storage system shutdown, or some fault of one or more software or hardware components within the storage system 124.

[0066] In one embodiment, controllers 125a, 125b operate as PCI masters to one or the other PCI buses 128a, 128b. In another embodiment, 128a and 128b may be based on other communications standards (e.g., HyperTransport, InfiBand, etc.). Other storage system embodiments may operate storage controllers 125a, 125b as multi-masters for both PCI buses 128a, 128b. Alternately, a PCI/NVMe/NVMf switching infrastructure or fabric may connect multiple storage controllers. Some storage system embodiments may allow storage devices to communicate with each other directly rather than communicating only with storage controllers. In one embodiment, a storage device controller 1 19a may be operable under direction from a storage controller 125a to synthesize and transfer data to be stored into Flash memory devices from data that has been stored in RAM (e.g., RAM 121 of Figure 1C). For example, a recalculated version of RAM content may be transferred after a storage controller has determined that an operation has fully committed across the storage system, or when fast- write memory on the device has reached a certain used capacity, or after a certain amount of time, to ensure improve safety of the data or to release addressable fast-write capacity for reuse. This mechanism may be used, for example, to avoid a second transfer over a bus (e.g., 128a, 128b) from the storage controllers 125a, 125b. In one embodiment, a recalculation may include compressing data, attaching indexing or other metadata, combining multiple data segments together, performing erasure code calculations, etc.

[0067] In one embodiment, under direction from a storage controller 125a, 125b, a storage device controller 1 19a, 119b may be operable to calculate and transfer data to other storage devices from data stored in RAM (e.g., RAM 121 of Figure 1C) without involvement of the storage controllers 125a, 125b. This operation may be used to mirror data stored in one controller 125a to another controller 125b, or it could be used to offload compression, data aggregation, and/or erasure coding calculations and transfers to storage devices to reduce load on storage controllers or the storage controller interface 129a, 129b to the PCI bus 128a, 128b.

[0068] A storage device controller 1 19 may include mechanisms for implementing high availability primitives for use by other parts of a storage system external to the Dual PCI storage device 1 18. For example, reservation or exclusion primitives may be provided so that, in a storage system with two storage controllers providing a highly available storage service, one storage controller may prevent the other storage controller from accessing or continuing to access the storage device. This could be used, for example, in cases where one controller detects that the other controller is not functioning properly or where the interconnect between the two storage controllers may itself not be functioning properly.

[0069] In one embodiment, a storage system for use with Dual PCI direct mapped storage devices with separately addressable fast write storage includes systems that manage erase blocks or groups of erase blocks as allocation units for storing data on behalf of the storage service, or for storing metadata (e.g., indexes, logs, etc.) associated with the storage service, or for proper management of the storage system itself. Flash pages, which may be a few kilobytes in size, may be written as data arrives or as the storage system is to persist data for long intervals of time (e.g., above a defined threshold of time). To commit data more quickly, or to reduce the number of writes to the Flash memory devices, the storage controllers may first write data into the separately addressable fast write storage on one more storage devices.

[0070] In one embodiment, the storage controllers 125a, 125b may initiate the use of erase blocks within and across storage devices (e.g., 1 18) in accordance with an age and expected remaining lifespan of the storage devices, or based on other statistics. The storage controllers 125a, 125b may initiate garbage collection and data migration data between storage devices in accordance with pages that are no longer needed as well as to manage Flash page and erase block lifespans and to manage overall system performance.

[0071] In one embodiment, the storage system 124 may utilize mirroring and/or erasure coding schemes as part of storing data into addressable fast write storage and/or as part of writing data into allocation units associated with erase blocks. Erasure codes may be used across storage devices, as well as within erase blocks or allocation units, or within and across Flash memory devices on a single storage device, to provide redundancy against single or multiple storage device failures or to protect against internal corruptions of Flash memory pages resulting from Flash memory operations or from degradation of Flash memory cells. Mirroring and erasure coding at various levels may be used to recover from multiple types of failures that occur separately or in combination.

[0072] The embodiments depicted with reference to Figs. 2A-G illustrate a storage cluster that stores user data, such as user data originating from one or more user or client systems or other sources external to the storage cluster. The storage cluster distributes user data across storage nodes housed within a chassis, or across multiple chassis, using erasure coding and redundant copies of metadata. Erasure coding refers to a method of data protection or reconstruction in which data is stored across a set of different locations, such as disks, storage nodes or geographic locations. Flash memory is one type of solid-state memory that may be integrated with the embodiments, although the embodiments may be extended to other types of solid-state memory or other storage medium, including non- solid state memory. Control of storage locations and workloads are distributed across the storage locations in a clustered peer-to-peer system. Tasks such as mediating communications between the various storage nodes, detecting when a storage node has become unavailable, and balancing I/Os (inputs and outputs) across the various storage nodes, are all handled on a distributed basis. Data is laid out or distributed across multiple storage nodes in data fragments or stripes that support data recovery in some embodiments. Ownership of data can be reassigned within a cluster, independent of input and output patterns. This architecture described in more detail below allows a storage node in the cluster to fail, with the system remaining operational, since the data can be reconstructed from other storage nodes and thus remain available for input and output operations. In various embodiments, a storage node may be referred to as a cluster node, a blade, or a server.

[0073] The storage cluster may be contained within a chassis, i.e., an enclosure housing one or more storage nodes. A mechanism to provide power to each storage node, such as a power distribution bus, and a communication mechanism, such as a communication bus that enables communication between the storage nodes are included within the chassis. The storage cluster can run as an independent system in one location according to some embodiments. In one embodiment, a chassis contains at least two instances of both the power distribution and the communication bus which may be enabled or disabled independently. The internal communication bus may be an Ethernet bus, however, other technologies such as Peripheral Component Interconnect (PCI) Express, InfiniBand, and others, are equally suitable. The chassis provides a port for an external communication bus for enabling communication between multiple chassis, directly or through a switch, and with client systems. The external communication may use a technology such as Ethernet, InfiniBand, Fibre Channel, etc. In some embodiments, the external communication bus uses different communication bus technologies for inter-chassis and client communication. If a switch is deployed within or between chassis, the switch may act as a translation between multiple protocols or technologies. When multiple chassis are connected to define a storage cluster, the storage cluster may be accessed by a client using either proprietary interfaces or standard interfaces such as network file system (NFS), common internet file system (CIFS), small computer system interface (SCSI) or hypertext transfer protocol (HTTP). Translation from the client protocol may occur at the switch, chassis external communication bus or within each storage node. In some embodiments, multiple chassis may be coupled or connected to each other through an aggregator switch. A portion and/or all of the coupled or connected chassis may be designated as a storage cluster. As discussed above, each chassis can have multiple blades, each blade has a MAC (media access control) address, but the storage cluster is presented to an external network as having a single cluster IP (Internet Protocol) address and a single MAC address in some embodiments.

[0074] Each storage node may be one or more storage servers and each storage server is connected to one or more non-volatile solid state memory units, which may be referred to as storage units or storage devices. One embodiment includes a single storage server in each storage node and between one to eight non-volatile solid state memory units, however this one example is not meant to be limiting. The storage server may include a processor, dynamic random access memory (DRAM) and interfaces for the internal communication bus and power distribution for each of the power buses. Inside the storage node, the interfaces and storage unit share a communication bus, e.g., PCI Express, in some embodiments. The non-volatile solid state memory units may directly access the internal communication bus interface through a storage node communication bus, or request the storage node to access the bus interface. The non-volatile solid state memory unit contains an embedded central processing unit (CPU), solid state storage controller, and a quantity of solid state mass storage, e.g., between 2-32 terabytes (TB) in some embodiments. An embedded volatile storage medium, such as DRAM, and an energy reserve apparatus are included in the nonvolatile solid state memory unit. In some embodiments, the energy reserve apparatus is a capacitor, super-capacitor, or battery that enables transferring a subset of DRAM contents to a stable storage medium in the case of power loss. In some embodiments, the non-volatile solid state memory unit is constructed with a storage class memory, such as phase change or magnetoresistive random access memory (MRAM) that substitutes for DRAM and enables a reduced power hold-up apparatus. [0075] One of many features of the storage nodes and non-volatile solid state storage is the ability to proactively rebuild data in a storage cluster. The storage nodes and non-volatile solid state storage can determine when a storage node or non-volatile solid state storage in the storage cluster is unreachable, independent of whether there is an attempt to read data involving that storage node or non-volatile solid state storage. The storage nodes and nonvolatile solid state storage then cooperate to recover and rebuild the data in at least partially new locations. This constitutes a proactive rebuild, in that the system rebuilds data without waiting until the data is needed for a read access initiated from a client system employing the storage cluster. These and further details of the storage memory and operation thereof are discussed below.

[0076] Fig. 2A is a perspective view of a storage cluster 161, with multiple storage nodes 150 and internal solid-state memory coupled to each storage node to provide network attached storage or storage area network, in accordance with some embodiments. A network attached storage, storage area network, or a storage cluster, or other storage memory, could include one or more storage clusters 161, each having one or more storage nodes 150, in a flexible and reconfigurable arrangement of both the physical components and the amount of storage memory provided thereby. The storage cluster 161 is designed to fit in a rack, and one or more racks can be set up and populated as desired for the storage memory. The storage cluster 161 has a chassis 138 having multiple slots 142. It should be appreciated that chassis 138 may be referred to as a housing, enclosure, or rack unit. In one embodiment, the chassis 138 has fourteen slots 142, although other numbers of slots are readily devised. For example, some embodiments have four slots, eight slots, sixteen slots, thirty-two slots, or other suitable number of slots. Each slot 142 can accommodate one storage node 150 in some

embodiments. Chassis 138 includes flaps 148 that can be utilized to mount the chassis 138 on a rack. Fans 144 provide air circulation for cooling of the storage nodes 150 and components thereof, although other cooling components could be used, or an embodiment could be devised without cooling components. A switch fabric 146 couples storage nodes 150 within chassis 138 together and to a network for communication to the memory. In an embodiment depicted in Fig. 1, the slots 142 to the left of the switch fabric 146 and fans 144 are shown occupied by storage nodes 150, while the slots 142 to the right of the switch fabric 146 and fans 144 are empty and available for insertion of storage node 150 for illustrative purposes. This configuration is one example, and one or more storage nodes 150 could occupy the slots 142 in various further arrangements. The storage node arrangements need not be sequential or adjacent in some embodiments. Storage nodes 150 are hot pluggable, meaning that a storage node 150 can be inserted into a slot 142 in the chassis 138, or removed from a slot 142, without stopping or powering down the system. Upon insertion or removal of storage node 150 from slot 142, the system automatically reconfigures in order to recognize and adapt to the change. Reconfiguration, in some embodiments, includes restoring redundancy and/or rebalancing data or load.

[0077] Each storage node 150 can have multiple components. In the embodiment shown here, the storage node 150 includes a printed circuit board 159 populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU 156, and a non-volatile solid state storage 152 coupled to the CPU 156, although other mountings and/or components could be used in further embodiments. The memory 154 has instructions which are executed by the CPU 156 and/or data operated on by the CPU 156. As further explained below, the non-volatile solid state storage 152 includes flash or, in further embodiments, other types of solid-state memory.

[0078] Referring to Fig. 2A, storage cluster 161 is scalable, meaning that storage capacity with non-uniform storage sizes is readily added, as described above. One or more storage nodes 150 can be plugged into or removed from each chassis and the storage cluster self- configures in some embodiments. Plug-in storage nodes 150, whether installed in a chassis as delivered or later added, can have different sizes. For example, in one embodiment a storage node 150 can have any multiple of 4 TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, a storage node 150 could have any multiple of other storage amounts or capacities. Storage capacity of each storage node 150 is broadcast, and influences decisions of how to stripe the data. For maximum storage efficiency, an embodiment can self- configure as wide as possible in the stripe, subject to a predetermined requirement of continued operation with loss of up to one, or up to two, non-volatile solid state storage units 152 or storage nodes 150 within the chassis.

[0079] Fig. 2B is a block diagram showing a communications interconnect 171 and power distribution bus 172 coupling multiple storage nodes 150. Referring back to Fig. 2A, the communications interconnect 171 can be included in or implemented with the switch fabric 146 in some embodiments. Where multiple storage clusters 161 occupy a rack, the communications interconnect 171 can be included in or implemented with a top of rack switch, in some embodiments. As illustrated in Fig. 2B, storage cluster 161 is enclosed within a single chassis 138. External port 176 is coupled to storage nodes 150 through communications interconnect 171, while external port 174 is coupled directly to a storage node. External power port 178 is coupled to power distribution bus 172. Storage nodes 150 may include varying amounts and differing capacities of non-volatile solid state storage 152 as described with reference to Fig. 2A. In addition, one or more storage nodes 150 may be a compute only storage node as illustrated in Fig. 2B. Authorities 168 are implemented on the non-volatile solid state storages 152, for example as lists or other data structures stored in memory. In some embodiments the authorities are stored within the non-volatile solid state storage 152 and supported by software executing on a controller or other processor of the non-volatile solid state storage 152. In a further embodiment, authorities 168 are implemented on the storage nodes 150, for example as lists or other data structures stored in the memory 154 and supported by software executing on the CPU 156 of the storage node 150. Authorities 168 control how and where data is stored in the non-volatile solid state storages 152 in some embodiments. This control assists in determining which type of erasure coding scheme is applied to the data, and which storage nodes 150 have which portions of the data. Each authority 168 may be assigned to a non-volatile solid state storage 152. Each authority may control a range of inode numbers, segment numbers, or other data identifiers which are assigned to data by a file system, by the storage nodes 150, or by the non-volatile solid state storage 152, in various embodiments.

[0080] Every piece of data, and every piece of metadata, has redundancy in the system in some embodiments. In addition, every piece of data and every piece of metadata has an owner, which may be referred to as an authority. If that authority is unreachable, for example through failure of a storage node, there is a plan of succession for how to find that data or that metadata. In various embodiments, there are redundant copies of authorities 168. Authorities 168 have a relationship to storage nodes 150 and non-volatile solid state storage 152 in some embodiments. Each authority 168, covering a range of data segment numbers or other identifiers of the data, may be assigned to a specific non-volatile solid state storage 152. In some embodiments the authorities 168 for all of such ranges are distributed over the nonvolatile solid state storages 152 of a storage cluster. Each storage node 150 has a network port that provides access to the non-volatile solid state storage(s) 152 of that storage node 150. Data can be stored in a segment, which is associated with a segment number and that segment number is an indirection for a configuration of a RAID (redundant array of independent disks) stripe in some embodiments. The assignment and use of the authorities 168 thus establishes an indirection to data. Indirection may be referred to as the ability to reference data indirectly, in this case via an authority 168, in accordance with some embodiments. A segment identifies a set of non-volatile solid state storage 152 and a local identifier into the set of non-volatile solid state storage 152 that may contain data. In some embodiments, the local identifier is an offset into the device and may be reused sequentially by multiple segments. In other embodiments the local identifier is unique for a specific segment and never reused. The offsets in the non-volatile solid state storage 152 are applied to locating data for writing to or reading from the non-volatile solid state storage 152 (in the form of a RAID stripe). Data is striped across multiple units of non-volatile solid state storage 152, which may include or be different from the non-volatile solid state storage 152 having the authority 168 for a particular data segment.

[0081] If there is a change in where a particular segment of data is located, e.g., during a data move or a data reconstruction, the authority 168 for that data segment should be consulted, at that non-volatile solid state storage 152 or storage node 150 having that authority 168. In order to locate a particular piece of data, embodiments calculate a hash value for a data segment or apply an inode number or a data segment number. The output of this operation points to a non-volatile solid state storage 152 having the authority 168 for that particular piece of data. In some embodiments there are two stages to this operation. The first stage maps an entity identifier (ID), e.g., a segment number, inode number, or directory number to an authority identifier. This mapping may include a calculation such as a hash or a bit mask. The second stage is mapping the authority identifier to a particular non-volatile solid state storage 152, which may be done through an explicit mapping. The operation is repeatable, so that when the calculation is performed, the result of the calculation repeatably and reliably points to a particular non-volatile solid state storage 152 having that authority 168. The operation may include the set of reachable storage nodes as input. If the set of reachable nonvolatile solid state storage units changes the optimal set changes. In some embodiments, the persisted value is the current assignment (which is always true) and the calculated value is the target assignment the cluster will attempt to reconfigure towards. This calculation may be used to determine the optimal non-volatile solid state storage 152 for an authority in the presence of a set of non-volatile solid state storage 152 that are reachable and constitute the same cluster. The calculation also determines an ordered set of peer non-volatile solid state storage 152 that will also record the authority to non-volatile solid state storage mapping so that the authority may be determined even if the assigned non-volatile solid state storage is unreachable. A duplicate or substitute authority 168 may be consulted if a specific authority 168 is unavailable in some embodiments.

[0082] With reference to Figs. 2A and 2B, two of the many tasks of the CPU 156 on a storage node 150 are to break up write data, and reassemble read data. When the system has determined that data is to be written, the authority 168 for that data is located as above. When the segment ID for data is already determined the request to write is forwarded to the non-volatile solid state storage 152 currently determined to be the host of the authority 168 determined from the segment. The host CPU 156 of the storage node 150, on which the nonvolatile solid state storage 152 and corresponding authority 168 reside, then breaks up or shards the data and transmits the data out to various non-volatile solid state storage 152. The transmitted data is written as a data stripe in accordance with an erasure coding scheme. In some embodiments, data is requested to be pulled, and in other embodiments, data is pushed. In reverse, when data is read, the authority 168 for the segment ID containing the data is located as described above. The host CPU 156 of the storage node 150 on which the nonvolatile solid state storage 152 and corresponding authority 168 reside requests the data from the non-volatile solid state storage and corresponding storage nodes pointed to by the authority. In some embodiments the data is read from flash storage as a data stripe. The host CPU 156 of storage node 150 then reassembles the read data, correcting any errors (if present) according to the appropriate erasure coding scheme, and forwards the reassembled data to the network. In further embodiments, some or all of these tasks can be handled in the non-volatile solid state storage 152. In some embodiments, the segment host requests the data be sent to storage node 150 by requesting pages from storage and then sending the data to the storage node making the original request.

[0083] In some systems, for example in UNIX-style file systems, data is handled with an index node or inode, which specifies a data structure that represents an object in a file system. The object could be a file or a directory, for example. Metadata may accompany the object, as attributes such as permission data and a creation timestamp, among other attributes. A segment number could be assigned to all or a portion of such an object in a file system. In other systems, data segments are handled with a segment number assigned elsewhere. For purposes of discussion, the unit of distribution is an entity, and an entity can be a file, a directory or a segment. That is, entities are units of data or metadata stored by a storage system. Entities are grouped into sets called authorities. Each authority has an authority owner, which is a storage node that has the exclusive right to update the entities in the authority. In other words, a storage node contains the authority, and that the authority, in turn, contains entities.

[0084] A segment is a logical container of data in accordance with some embodiments. A segment is an address space between medium address space and physical flash locations, i.e., the data segment number, are in this address space. Segments may also contain meta-data, which enable data redundancy to be restored (rewritten to different flash locations or devices) without the involvement of higher level software. In one embodiment, an internal format of a segment contains client data and medium mappings to determine the position of that data. Each data segment is protected, e.g., from memory and other failures, by breaking the segment into a number of data and parity shards, where applicable. The data and parity shards are distributed, i.e., striped, across non-volatile solid state storage 152 coupled to the host CPUs 156 (See Figs. 2E and 2G) in accordance with an erasure coding scheme. Usage of the term segments refers to the container and its place in the address space of segments in some embodiments. Usage of the term stripe refers to the same set of shards as a segment and includes how the shards are distributed along with redundancy or parity information in accordance with some embodiments.

[0085] A series of address-space transformations takes place across an entire storage system. At the top are the directory entries (file names) which link to an inode. Inodes point into medium address space, where data is logically stored. Medium addresses may be mapped through a series of indirect mediums to spread the load of large files, or implement data services like deduplication or snapshots. Medium addresses may be mapped through a series of indirect mediums to spread the load of large files, or implement data services like deduplication or snapshots. Segment addresses are then translated into physical flash locations. Physical flash locations have an address range bounded by the amount of flash in the system in accordance with some embodiments. Medium addresses and segment addresses are logical containers, and in some embodiments use a 128 bit or larger identifier so as to be practically infinite, with a likelihood of reuse calculated as longer than the expected life of the system. Addresses from logical containers are allocated in a hierarchical fashion in some embodiments. Initially, each non-volatile solid state storage unit 152 may be assigned a range of address space. Within this assigned range, the non-volatile solid state storage 152 is able to allocate addresses without synchronization with other non-volatile solid state storage 152.

[0086] Data and metadata is stored by a set of underlying storage layouts that are optimized for varying workload patterns and storage devices. These layouts incorporate multiple redundancy schemes, compression formats and index algorithms. Some of these layouts store information about authorities and authority masters, while others store file metadata and file data. The redundancy schemes include error correction codes that tolerate corrupted bits within a single storage device (such as a NAND flash chip), erasure codes that tolerate the failure of multiple storage nodes, and replication schemes that tolerate data center or regional failures. In some embodiments, low density parity check (LDPC) code is used within a single storage unit. Reed-Solomon encoding is used within a storage cluster, and mirroring is used within a storage grid in some embodiments. Metadata may be stored using an ordered log structured index (such as a Log Structured Merge Tree), and large data may not be stored in a log structured layout.

[0087] In order to maintain consistency across multiple copies of an entity, the storage nodes agree implicitly on two things through calculations: (1) the authority that contains the entity, and (2) the storage node that contains the authority. The assignment of entities to authorities can be done by pseudo randomly assigning entities to authorities, by splitting entities into ranges based upon an externally produced key, or by placing a single entity into each authority. Examples of pseudorandom schemes are linear hashing and the Replication Under Scalable Hashing (RUSH) family of hashes, including Controlled Replication Under Scalable Hashing (CRUSH). In some embodiments, pseudo-random assignment is utilized only for assigning authorities to nodes because the set of nodes can change. The set of authorities cannot change so any subjective function may be applied in these embodiments. Some placement schemes automatically place authorities on storage nodes, while other placement schemes rely on an explicit mapping of authorities to storage nodes. In some embodiments, a pseudorandom scheme is utilized to map from each authority to a set of candidate authority owners. A pseudorandom data distribution function related to CRUSH may assign authorities to storage nodes and create a list of where the authorities are assigned. Each storage node has a copy of the pseudorandom data distribution function, and can arrive at the same calculation for distributing, and later finding or locating an authority. Each of the pseudorandom schemes requires the reachable set of storage nodes as input in some embodiments in order to conclude the same target nodes. Once an entity has been placed in an authority, the entity may be stored on physical devices so that no expected failure will lead to unexpected data loss. In some embodiments, rebalancing algorithms attempt to store the copies of all entities within an authority in the same layout and on the same set of machines.

[0088] Examples of expected failures include device failures, stolen machines, datacenter fires, and regional disasters, such as nuclear or geological events. Different failures lead to different levels of acceptable data loss. In some embodiments, a stolen storage node impacts neither the security nor the reliability of the system, while depending on system

configuration, a regional event could lead to no loss of data, a few seconds or minutes of lost updates, or even complete data loss.

[0089] In the embodiments, the placement of data for storage redundancy is independent of the placement of authorities for data consistency. In some embodiments, storage nodes that contain authorities do not contain any persistent storage. Instead, the storage nodes are connected to non-volatile solid state storage units that do not contain authorities. The communications interconnect between storage nodes and non-volatile solid state storage units consists of multiple communication technologies and has non-uniform performance and fault tolerance characteristics. In some embodiments, as mentioned above, non-volatile solid state storage units are connected to storage nodes via PCI express, storage nodes are connected together within a single chassis using Ethernet backplane, and chassis are connected together to form a storage cluster. Storage clusters are connected to clients using Ethernet or fiber channel in some embodiments. If multiple storage clusters are configured into a storage grid, the multiple storage clusters are connected using the Internet or other long-distance networking links, such as a "metro scale" link or private link that does not traverse the internet.

[0090] Authority owners have the exclusive right to modify entities, to migrate entities from one non- volatile solid state storage unit to another non-volatile solid state storage unit, and to add and remove copies of entities. This allows for maintaining the redundancy of the underlying data. When an authority owner fails, is going to be decommissioned, or is overloaded, the authority is transferred to a new storage node. Transient failures make it non- trivial to ensure that all non-faulty machines agree upon the new authority location. The ambiguity that arises due to transient failures can be achieved automatically by a consensus protocol such as Paxos, hot-warm failover schemes, via manual intervention by a remote system administrator, or by a local hardware administrator (such as by physically removing the failed machine from the cluster, or pressing a button on the failed machine). In some embodiments, a consensus protocol is used, and failover is automatic. If too many failures or replication events occur in too short a time period, the system goes into a self-preservation mode and halts replication and data movement activities until an administrator intervenes in accordance with some embodiments.

[0091] As authorities are transferred between storage nodes and authority owners update entities in their authorities, the system transfers messages between the storage nodes and nonvolatile solid state storage units. With regard to persistent messages, messages that have different purposes are of different types. Depending on the type of the message, the system maintains different ordering and durability guarantees. As the persistent messages are being processed, the messages are temporarily stored in multiple durable and non-durable storage hardware technologies. In some embodiments, messages are stored in RAM, NVRAM and on NAND flash devices, and a variety of protocols are used in order to make efficient use of each storage medium. Latency-sensitive client requests may be persisted in replicated NVRAM, and then later NAND, while background rebalancing operations are persisted directly to NAND.

[0092] Persistent messages are persistently stored prior to being transmitted. This allows the system to continue to serve client requests despite failures and component replacement. Although many hardware components contain unique identifiers that are visible to system administrators, manufacturer, hardware supply chain and ongoing monitoring quality control infrastructure, applications running on top of the infrastructure address virtualize addresses. These virtualized addresses do not change over the lifetime of the storage system, regardless of component failures and replacements. This allows each component of the storage system to be replaced over time without reconfiguration or disruptions of client request processing, i.e., the system supports non-disruptive upgrades.

[0093] In some embodiments, the virtualized addresses are stored with sufficient redundancy. A continuous monitoring system correlates hardware and software status and the hardware identifiers. This allows detection and prediction of failures due to faulty components and manufacturing details. The monitoring system also enables the proactive transfer of authorities and entities away from impacted devices before failure occurs by removing the component from the critical path in some embodiments.

[0094] Fig. 2C is a multiple level block diagram, showing contents of a storage node 150 and contents of a non-volatile solid state storage 152 of the storage node 150. Data is communicated to and from the storage node 150 by a network interface controller (NIC) 202 in some embodiments. Each storage node 150 has a CPU 156, and one or more non-volatile solid state storage 152, as discussed above. Moving down one level in Fig. 2C, each nonvolatile solid state storage 152 has a relatively fast non-volatile solid state memory, such as nonvolatile random access memory (NVRAM) 204, and flash memory 206. In some embodiments, NVRAM 204 may be a component that does not require program/erase cycles (DRAM, MRAM, PCM), and can be a memory that can support being written vastly more often than the memory is read from. Moving down another level in Fig. 2C, the NVRAM 204 is implemented in one embodiment as high speed volatile memory, such as dynamic random access memory (DRAM) 216, backed up by energy reserve 218. Energy reserve 218 provides sufficient electrical power to keep the DRAM 216 powered long enough for contents to be transferred to the flash memory 206 in the event of power failure. In some embodiments, energy reserve 218 is a capacitor, super-capacitor, battery, or other device, that supplies a suitable supply of energy sufficient to enable the transfer of the contents of DRAM 216 to a stable storage medium in the case of power loss. The flash memory 206 is implemented as multiple flash dies 222, which may be referred to as packages of flash dies 222 or an array of flash dies 222. It should be appreciated that the flash dies 222 could be packaged in any number of ways, with a single die per package, multiple dies per package (i.e. multichip packages), in hybrid packages, as bare dies on a printed circuit board or other substrate, as encapsulated dies, etc. In the embodiment shown, the non-volatile solid state storage 152 has a controller 212 or other processor, and an input output (I/O) port 210 coupled to the controller 212. I/O port 210 is coupled to the CPU 156 and/or the network interface controller 202 of the flash storage node 150. Flash input output (I/O) port 220 is coupled to the flash dies 222, and a direct memory access unit (DMA) 214 is coupled to the controller 212, the DRAM 216 and the flash dies 222. In the embodiment shown, the I/O port 210, controller 212, DMA unit 214 and flash I/O port 220 are implemented on a programmable logic device (PLD) 208, e.g., a field programmable gate array (FPGA). In this embodiment, each flash die 222 has pages, organized as sixteen kB (kilobyte) pages 224, and a register 226 through which data can be written to or read from the flash die 222. In further embodiments, other types of solid-state memory are used in place of, or in addition to flash memory illustrated within flash die 222.

[0095] Storage clusters 161, in various embodiments as disclosed herein, can be contrasted with storage arrays in general. The storage nodes 150 are part of a collection that creates the storage cluster 161. Each storage node 150 owns a slice of data and computing required to provide the data. Multiple storage nodes 150 cooperate to store and retrieve the data.

Storage memory or storage devices, as used in storage arrays in general, are less involved with processing and manipulating the data. Storage memory or storage devices in a storage array receive commands to read, write, or erase data. The storage memory or storage devices in a storage array are not aware of a larger system in which they are embedded, or what the data means. Storage memory or storage devices in storage arrays can include various types of storage memory, such as RAM, solid state drives, hard disk drives, etc. The storage units 152 described herein have multiple interfaces active simultaneously and serving multiple purposes. In some embodiments, some of the functionality of a storage node 150 is shifted into a storage unit 152, transforming the storage unit 152 into a combination of storage unit 152 and storage node 150. Placing computing (relative to storage data) into the storage unit 152 places this computing closer to the data itself. The various system embodiments have a hierarchy of storage node layers with different capabilities. By contrast, in a storage array, a controller owns and knows everything about all of the data that the controller manages in a shelf or storage devices. In a storage cluster 161, as described herein, multiple controllers in multiple storage units 152 and/or storage nodes 150 cooperate in various ways (e.g., for erasure coding, data sharding, metadata communication and redundancy, storage capacity expansion or contraction, data recovery, and so on).

[0096] Fig. 2D shows a storage server environment, which uses embodiments of the storage nodes 150 and storage units 152 of Figs. 2A-C. In this version, each storage unit 152 has a processor such as controller 212 (see Fig. 2C), an FPGA (field programmable gate array), flash memory 206, and NVRAM 204 (which is super-capacitor backed DRAM 216, see Figs. 2B and 2C) on a PCIe (peripheral component interconnect express) board in a chassis 138 (see Fig. 2A). The storage unit 152 may be implemented as a single board containing storage, and may be the largest tolerable failure domain inside the chassis. In some embodiments, up to two storage units 152 may fail and the device will continue with no data loss.

[0097] The physical storage is divided into named regions based on application usage in some embodiments. The NVRAM 204 is a contiguous block of reserved memory in the storage unit 152 DRAM 216, and is backed by NAND flash. NVRAM 204 is logically divided into multiple memory regions written for two as spool (e.g., spool_region). Space within the NVRAM 204 spools is managed by each authority 168 independently. Each device provides an amount of storage space to each authority 168. That authority 168 further manages lifetimes and allocations within that space. Examples of a spool include distributed transactions or notions. When the primary power to a storage unit 152 fails, onboard super- capacitors provide a short duration of power hold up. During this holdup interval, the contents of the NVRAM 204 are flushed to flash memory 206. On the next power-on, the contents of the NVRAM 204 are recovered from the flash memory 206.

[0098] As for the storage unit controller, the responsibility of the logical "controller" is distributed across each of the blades containing authorities 168. This distribution of logical control is shown in Fig. 2D as a host controller 242, mid-tier controller 244 and storage unit controller(s) 246. Management of the control plane and the storage plane are treated independently, although parts may be physically co-located on the same blade. Each authority 168 effectively serves as an independent controller. Each authority 168 provides its own data and metadata structures, its own background workers, and maintains its own lifecycle.

[0099] Fig. 2E is a blade 252 hardware block diagram, showing a control plane 254, compute and storage planes 256, 258, and authorities 168 interacting with underlying physical resources, using embodiments of the storage nodes 150 and storage units 152 of Figs. 2A-C in the storage server environment of Fig. 2D. The control plane 254 is partitioned into a number of authorities 168 which can use the compute resources in the compute plane 256 to run on any of the blades 252. The storage plane 258 is partitioned into a set of devices, each of which provides access to flash 206 and NVRAM 204 resources.

[00100] In the compute and storage planes 256, 258 of Fig. 2E, the authorities 168 interact with the underlying physical resources (i.e., devices). From the point of view of an authority 168, its resources are striped over all of the physical devices. From the point of view of a device, it provides resources to all authorities 168, irrespective of where the authorities happen to run. Each authority 168 has allocated or has been allocated one or more partitions 260 of storage memory in the storage units 152, e.g. partitions 260 in flash memory 206 and NVRAM 204. Each authority 168 uses those allocated partitions 260 that belong to it, for writing or reading user data. Authorities can be associated with differing amounts of physical storage of the system. For example, one authority 168 could have a larger number of partitions 260 or larger sized partitions 260 in one or more storage units 152 than one or more other authorities 168.

[00101] Fig. 2F depicts elasticity software layers in blades 252 of a storage cluster 161, in accordance with some embodiments. In the elasticity structure, elasticity software is symmetric, i.e., each blade's compute module 270 runs the three identical layers of processes depicted in Fig. 2F. Storage managers 274 execute read and write requests from other blades 252 for data and metadata stored in local storage unit 152 NVRAM 204 and flash 206.

Authorities 168 fulfill client requests by issuing the necessary reads and writes to the blades 252 on whose storage units 152 the corresponding data or metadata resides. Endpoints 272 parse client connection requests received from switch fabric 146 supervisory software, relay the client connection requests to the authorities 168 responsible for fulfillment, and relay the authorities' 168 responses to clients. The symmetric three-layer structure enables the storage system's high degree of concurrency. Elasticity scales out efficiently and reliably in these embodiments. In addition, elasticity implements a unique scale -out technique that balances work evenly across all resources regardless of client access pattern, and maximizes concurrency by eliminating much of the need for inter-blade coordination that typically occurs with conventional distributed locking.

[00102] Still referring to Fig. 2F, authorities 168 running in the compute modules 270 of a blade 252 perform the internal operations required to fulfill client requests. One feature of elasticity is that authorities 168 are stateless, i.e., they cache active data and metadata in their own blades' 168 DRAMs for fast access, but the authorities store every update in their NVRAM 204 partitions on three separate blades 252 until the update has been written to flash 206. All the storage system writes to NVRAM 204 are in triplicate to partitions on three separate blades 252 in some embodiments. With triple-mirrored NVRAM 204 and persistent storage protected by parity and Reed-Solomon RAID checksums, the storage system can survive concurrent failure of two blades 252 with no loss of data, metadata, or access to either.

[00103] Because authorities 168 are stateless, they can migrate between blades 252. Each authority 168 has a unique identifier. NVRAM 204 and flash 206 partitions are associated with authorities' 168 identifiers, not with the blades 252 on which they are running in some . Thus, when an authority 168 migrates, the authority 168 continues to manage the same storage partitions from its new location. When a new blade 252 is installed in an

embodiment of the storage cluster 161, the system automatically rebalances load by:

Partitioning the new blade's 252 storage for use by the system's authorities 168,

Migrating selected authorities 168 to the new blade 252,

Starting endpoints 272 on the new blade 252 and including them in the switch fabric's 146 client connection distribution algorithm.

[00104] From their new locations, migrated authorities 168 persist the contents of their NVRAM 204 partitions on flash 206, process read and write requests from other authorities 168, and fulfill the client requests that endpoints 272 direct to them. Similarly, if a blade 252 fails or is removed, the system redistributes its authorities 168 among the system's remaining blades 252. The redistributed authorities 168 continue to perform their original functions from their new locations.

[00105] Fig. 2G depicts authorities 168 and storage resources in blades 252 of a storage cluster, in accordance with some embodiments. Each authority 168 is exclusively responsible for a partition of the flash 206 and NVRAM 204 on each blade 252. The authority 168 manages the content and integrity of its partitions independently of other authorities 168. Authorities 168 compress incoming data and preserve it temporarily in their NVRAM 204 partitions, and then consolidate, RAID-protect, and persist the data in segments of the storage in their flash 206 partitions. As the authorities 168 write data to flash 206, storage managers 274 perform the necessary flash translation to optimize write performance and maximize media longevity. In the background, authorities 168 "garbage collect," or reclaim space occupied by data that clients have made obsolete by overwriting the data. It should be appreciated that since authorities' 168 partitions are disjoint, there is no need for distributed locking to execute client and writes or to perform background functions.

[00106] The embodiments described herein may utilize various software, communication and/or networking protocols. In addition, the configuration of the hardware and/or software may be adjusted to accommodate various protocols. For example, the embodiments may utilize Active Directory, which is a database based system that provides authentication, directory, policy, and other services in a WINDOWSTM environment. In these

embodiments, LDAP (Lightweight Directory Access Protocol) is one example application protocol for querying and modifying items in directory service providers such as Active Directory. In some embodiments, a network lock manager (NLM) is utilized as a facility that works in cooperation with the Network File System (NFS) to provide a System V style of advisory file and record locking over a network. The Server Message Block (SMB) protocol, one version of which is also known as Common Internet File System (CIFS), may be integrated with the storage systems discussed herein. SMP operates as an application-layer network protocol typically used for providing shared access to files, printers, and serial ports and miscellaneous communications between nodes on a network. SMB also provides an authenticated inter-process communication mechanism. AMAZONTM S3 (Simple Storage Service) is a web service offered by Amazon Web Services, and the systems described herein may interface with Amazon S3 through web services interfaces (REST (representational state transfer), SOAP (simple object access protocol), and BitTorrent). A RESTful API

(application programming interface) breaks down a transaction to create a series of small modules. Each module addresses a particular underlying part of the transaction. The control or permissions provided with these embodiments, especially for object data, may include utilization of an access control list (ACL). The ACL is a list of permissions attached to an object and the ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. The systems may utilize Internet Protocol version 6 (IPv6), as well as IPv4, for the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. The routing of packets between networked systems may include Equal-cost multi- path routing (ECMP), which is a routing strategy where next-hop packet forwarding to a single destination can occur over multiple "best paths" which tie for top place in routing metric calculations. Multi-path routing can be used in conjunction with most routing protocols, because it is a per-hop decision limited to a single router. The software may support Multi-tenancy, which is an architecture in which a single instance of a software application serves multiple customers. Each customer may be referred to as a tenant. Tenants may be given the ability to customize some parts of the application, but may not customize the application's code, in some embodiments. The embodiments may maintain audit logs. An audit log is a document that records an event in a computing system. In addition to documenting what resources were accessed, audit log entries typically include destination and source addresses, a timestamp, and user login information for compliance with various regulations. The embodiments may support various key management policies, such as encryption key rotation. In addition, the system may support dynamic root passwords or some variation dynamically changing passwords.

[00107] Figure 3A sets forth a diagram of a storage system 306 that is coupled for data communications with a cloud services provider 302 in accordance with some embodiments of the present disclosure. Although depicted in less detail, the storage system 306 depicted in Figure 3A may be similar to the storage systems described above with reference to Figures 1A-1D and Figures 2A-2G. In some embodiments, the storage system 306 depicted in Figure 3A may be embodied as a storage system that includes imbalanced active/active controllers, as a storage system that includes balanced active/active controllers, as a storage system that includes active/active controllers where less than all of each controller's resources are utilized such that each controller has reserve resources that may be used to support failover, as a storage system that includes fully active/active controllers, as a storage system that includes dataset-segregated controllers, as a storage system that includes dual-layer architectures with front-end controllers and back-end integrated storage controllers, as a storage system that includes scale-out clusters of dual -controller arrays, as well as combinations of such embodiments.

[00108] In the example depicted in Figure 3A, the storage system 306 is coupled to the cloud services provider 302 via a data communications link 304. The data communications link 304 may be embodied as a dedicated data communications link, as a data communications pathway that is provided through the use of one or data communications networks such as a wide area network ('WAN') or local area network ('LAN'), or as some other mechanism capable of transporting digital information between the storage system 306 and the cloud services provider 302. Such a data communications link 304 may be fully wired, fully wireless, or some aggregation of wired and wireless data communications pathways. In such an example, digital information may be exchanged between the storage system 306 and the cloud services provider 302 via the data communications link 304 using one or more data communications protocols. For example, digital information may be exchanged between the storage system 306 and the cloud services provider 302 via the data communications link 304 using the handheld device transfer protocol ('HDTP'), hypertext transfer protocol ('HTTP'), internet protocol ('IP'), real-time transfer protocol ('RTP'), transmission control protocol ('TCP'), user datagram protocol ('UDP'), wireless application protocol ('WAP'), or other protocol.

[00109] The cloud services provider 302 depicted in Figure 3A may be embodied, for example, as a system and computing environment that provides services to users of the cloud services provider 302 through the sharing of computing resources via the data

communications link 304. The cloud services provider 302 may provide on-demand access to a shared pool of configurable computing resources such as computer networks, servers, storage, applications and services, and so on. The shared pool of configurable resources may be rapidly provisioned and released to a user of the cloud services provider 302 with minimal management effort. Generally, the user of the cloud services provider 302 is unaware of the exact computing resources utilized by the cloud services provider 302 to provide the services. Although in many cases such a cloud services provider 302 may be accessible via the Internet, readers of skill in the art will recognize that any system that abstracts the use of shared resources to provide services to a user through any data communications link may be considered a cloud services provider 302.

[00110] In the example depicted in Figure 3A, the cloud services provider 302 may be configured to provide a variety of services to the storage system 306 and users of the storage system 306 through the implementation of various service models. For example, the cloud services provider 302 may be configured to provide services to the storage system 306 and users of the storage system 306 through the implementation of an infrastructure as a service ('IaaS') service model where the cloud services provider 302 offers computing infrastructure such as virtual machines and other resources as a service to subscribers. In addition, the cloud services provider 302 may be configured to provide services to the storage system 306 and users of the storage system 306 through the implementation of a platform as a service ('PaaS') service model where the cloud services provider 302 offers a development environment to application developers. Such a development environment may include, for example, an operating system, programming-language execution environment, database, web server, or other components that may be utilized by application developers to develop and run software solutions on a cloud platform. Furthermore, the cloud services provider 302 may be configured to provide services to the storage system 306 and users of the storage system 306 through the implementation of a software as a service ('SaaS') service model where the cloud services provider 302 offers application software, databases, as well as the platforms that are used to run the applications to the storage system 306 and users of the storage system 306, providing the storage system 306 and users of the storage system 306 with on-demand software and eliminating the need to install and run the application on local computers, which may simplify maintenance and support of the application. The cloud services provider 302 may be further configured to provide services to the storage system 306 and users of the storage system 306 through the implementation of an authentication as a service ('AaaS') service model where the cloud services provider 302 offers authentication services that can be used to secure access to applications, data sources, or other resources. The cloud services provider 302 may also be configured to provide services to the storage system 306 and users of the storage system 306 through the implementation of a storage as a service service model where the cloud services provider 302 offers access to its storage infrastructure for use by the storage system 306 and users of the storage system 306. Readers will appreciate that the cloud services provider 302 may be configured to provide additional services to the storage system 306 and users of the storage system 306 through the implementation of additional service models, as the service models described above are included only for explanatory purposes and in no way represent a limitation of the services that may be offered by the cloud services provider 302 or a limitation as to the service models that may be implemented by the cloud services provider 302.

[00111] In the example depicted in Figure 3A, the cloud services provider 302 may be embodied, for example, as a private cloud, as a public cloud, or as a combination of a private cloud and public cloud. In an embodiment in which the cloud services provider 302 is embodied as a private cloud, the cloud services provider 302 may be dedicated to providing services to a single organization rather than providing services to multiple organizations. In an embodiment where the cloud services provider 302 is embodied as a public cloud, the cloud services provider 302 may provide services to multiple organizations. Public cloud and private cloud deployment models may differ and may come with various advantages and disadvantages. For example, because a public cloud deployment involves the sharing of a computing infrastructure across different organization, such a deployment may not be ideal for organizations with security concerns, mission-critical workloads, uptime requirements demands, and so on. While a private cloud deployment can address some of these issues, a private cloud deployment may require on-premises staff to manage the private cloud. In still alternative embodiments, the cloud services provider 302 may be embodied as a mix of a private and public cloud services with a hybrid cloud deployment. [00112] Although not explicitly depicted in Figure 3 A, readers will appreciate that additional hardware components and additional software components may be necessary to facilitate the delivery of cloud services to the storage system 306 and users of the storage system 306. For example, the storage system 306 may be coupled to (or even include) a cloud storage gateway. Such a cloud storage gateway may be embodied, for example, as hardware -based or software-based appliance that is located on premise with the storage system 306. Such a cloud storage gateway may operate as a bridge between local applications that are executing on the storage array 306 and remote, cloud-based storage that is utilized by the storage array 306. Through the use of a cloud storage gateway, organizations may move primary iSCSI or NAS to the cloud services provider 302, thereby enabling the organization to save space on their on-premises storage systems. Such a cloud storage gateway may be configured to emulate a disk array, a block-based device, a file server, or other storage system that can translate the SCSI commands, file server commands, or other appropriate command into REST-space protocols that facilitate communications with the cloud services provider 302.

[00113] In order to enable the storage system 306 and users of the storage system 306 to make use of the services provided by the cloud services provider 302, a cloud migration process may take place during which data, applications, or other elements from an organization's local systems (or even from another cloud environment) are moved to the cloud services provider 302. In order to successfully migrate data, applications, or other elements to the cloud services provider's 302 environment, middleware such as a cloud migration tool may be utilized to bridge gaps between the cloud services provider's 302 environment and an organization's environment. Such cloud migration tools may also be configured to address potentially high network costs and long transfer times associated with migrating large volumes of data to the cloud services provider 302, as well as addressing security concerns associated with sensitive data to the cloud services provider 302 over data communications networks. In order to further enable the storage system 306 and users of the storage system 306 to make use of the services provided by the cloud services provider 302, a cloud orchestrator may also be used to arrange and coordinate automated tasks in pursuit of creating a consolidated process or workflow. Such a cloud orchestrator may perform tasks such as configuring various components, whether those components are cloud components or on-premises components, as well as managing the interconnections between such components. The cloud orchestrator can simplify the inter-component communication and connections to ensure that links are correctly configured and maintained. [00114] In the example depicted in Figure 3 A, and as described briefly above, the cloud services provider 302 may be configured to provide services to the storage system 306 and users of the storage system 306 through the usage of a SaaS service model where the cloud services provider 302 offers application software, databases, as well as the platforms that are used to run the applications to the storage system 306 and users of the storage system 306, providing the storage system 306 and users of the storage system 306 with on-demand software and eliminating the need to install and run the application on local computers, which may simplify maintenance and support of the application. Such applications may take many forms in accordance with various embodiments of the present disclosure. For example, the cloud services provider 302 may be configured to provide access to data analytics applications to the storage system 306 and users of the storage system 306. Such data analytics applications may be configured, for example, to receive telemetry data phoned home by the storage system 306. Such telemetry data may describe various operating characteristics of the storage system 306 and may be analyzed, for example, to determine the health of the storage system 306, to identify workloads that are executing on the storage system 306, to predict when the storage system 306 will run out of various resources, to recommend configuration changes, hardware or software upgrades, workflow migrations, or other actions that may improve the operation of the storage system 306.

[00115] The cloud services provider 302 may also be configured to provide access to virtualized computing environments to the storage system 306 and users of the storage system 306. Such virtualized computing environments may be embodied, for example, as a virtual machine or other virtualized computer hardware platforms, virtual storage devices, virtualized computer network resources, and so on. Examples of such virtualized environments can include virtual machines that are created to emulate an actual computer, virtualized desktop environments that separate a logical desktop from a physical machine, virtualized file systems that allow uniform access to different types of concrete file systems, and many others.

[00116] For further explanation, Figure 3B sets forth a diagram of a storage system 306 in accordance with some embodiments of the present disclosure. Although depicted in less detail, the storage system 306 depicted in Figure 3B may be similar to the storage systems described above with reference to Figures 1A-1D and Figures 2A-2G as the storage system may include many of the components described above.

[00117] The storage system 306 depicted in Figure 3B may include storage resources 308, which may be embodied in many forms. For example, in some embodiments the storage resources 308 can include nano-RAM or another form of nonvolatile random access memory that utilizes carbon nanotubes deposited on a substrate. In some embodiments, the storage resources 308 may include 3D crosspoint non-volatile memory in which bit storage is based on a change of bulk resistance, in conjunction with a stackable cross-gridded data access array. In some embodiments, the storage resources 308 may include flash memory, including single-level cell ('SLC') NAND flash, multi-level cell ('MLC') NAND flash, triple-level cell ( LC) NAND flash, quad-level cell ('QLC') NAND flash, and others. In some embodiments, the storage resources 308 may include non-volatile magnetore si stive random- access memory ('MRAM'), including spin transfer torque ('STT') MRAM, in which data is stored through the use of magnetic storage elements. In some embodiments, the example storage resources 308 may include non-volatile phase-change memory ('PCM') that may have the ability to hold multiple bits in a single cell as cells can achieve a number of distinct intermediary states. In some embodiments, the storage resources 308 may include quantum memory that allows for the storage and retrieval of photonic quantum information. In some embodiments, the example storage resources 308 may include resistive random-access memory ('ReRAM') in which data is stored by changing the resistance across a dielectric solid-state material. In some embodiments, the storage resources 308 may include storage class memory ('SCM') in which solid-state nonvolatile memory may be manufactured at a high density using some combination of sub-lithographic patterning techniques, multiple bits per cell, multiple layers of devices, and so on. Readers will appreciate that other forms of computer memories and storage devices may be utilized by the storage systems described above, including DRAM, SRAM, EEPROM, universal memory, and many others. The storage resources 308 depicted in Figure 3A may be embodied in a variety of form factors, including but not limited to, dual in-line memory modules ('DIMMs'), non-volatile dual inline memory modules ('NVDIMMs'), M.2, U.2, and others.

[00118] The example storage system 306 depicted in Figure 3B may implement a variety of storage architectures. For example, storage systems in accordance with some embodiments of the present disclosure may utilize block storage where data is stored in blocks, and each block essentially acts as an individual hard drive. Storage systems in accordance with some embodiments of the present disclosure may utilize object storage, where data is managed as objects. Each object may include the data itself, a variable amount of metadata, and a globally unique identifier, where object storage can be implemented at multiple levels (e.g., device level, system level, interface level). Storage systems in accordance with some embodiments of the present disclosure utilize file storage in which data is stored in a hierarchical structure. Such data may be saved in files and folders, and presented to both the system storing it and the system retrieving it in the same format.

[00119] The example storage system 306 depicted in Figure 3B may be embodied as a storage system in which additional storage resources can be added through the use of a scale- up model, additional storage resources can be added through the use of a scale-out model, or through some combination thereof. In a scale-up model, additional storage may be added by adding additional storage devices. In a scale-out model, however, additional storage nodes may be added to a cluster of storage nodes, where such storage nodes can include additional processing resources, additional networking resources, and so on.

[00120] The storage system 306 depicted in Figure 3B also includes communications resources 310 that may be useful in facilitating data communications between components within the storage system 306, as well as data communications between the storage system 306 and computing devices that are outside of the storage system 306. The communications resources 310 may be configured to utilize a variety of different protocols and data communication fabrics to facilitate data communications between components within the storage systems as well as computing devices that are outside of the storage system. For example, the communications resources 310 can include fibre channel ('FC') technologies such as FC fabrics and FC protocols that can transport SCSI commands over FC networks. The communications resources 310 can also include FC over ethernet ('FCoE') technologies through which FC frames are encapsulated and transmitted over Ethernet networks. The communications resources 310 can also include InfiniBand ('IB') technologies in which a switched fabric topology is utilized to facilitate transmissions between channel adapters. The communications resources 310 can also include NVM Express ('NVMe') technologies and NVMe over fabrics ('NVMeoF') technologies through which non-volatile storage media attached via a PCI express ('PCIe') bus may be accessed. The communications resources 310 can also include mechanisms for accessing storage resources 308 within the storage system 306 utilizing serial attached SCSI ('SAS'), serial ATA ('SATA') bus interfaces for connecting storage resources 308 within the storage system 306 to host bus adapters within the storage system 306, internet small computer systems interface ('iSCSF) technologies to provide block-level access to storage resources 308 within the storage system 306, and other communications resources that that may be useful in facilitating data communications between components within the storage system 306, as well as data communications between the storage system 306 and computing devices that are outside of the storage system 306. [00121] The storage system 306 depicted in Figure 3B also includes processing resources 312 that may be useful in useful in executing computer program instructions and performing other computational tasks within the storage system 306. The processing resources 312 may include one or more application-specific integrated circuits ('ASICs') that are customized for some particular purpose as well as one or more central processing units ('CPUs'). The processing resources 312 may also include one or more digital signal processors ('DSPs'), one or more field-programmable gate arrays ('FPGAs'), one or more systems on a chip ('SoCs'), or other form of processing resources 312. The storage system 306 may utilize the storage resources 312 to perform a variety of tasks including, but not limited to, supporting the execution of software resources 314 that will be described in greater detail below.

[00122] The storage system 306 depicted in Figure 3B also includes software resources 314 that, when executed by processing resources 312 within the storage system 306, may perform various tasks. The software resources 314 may include, for example, one or more modules of computer program instructions that when executed by processing resources 312 within the storage system 306 are useful in carrying out various data protection techniques to preserve the integrity of data that is stored within the storage systems. Readers will appreciate that such data protection techniques may be carried out, for example, by system software executing on computer hardware within the storage system, by a cloud services provider, or in other ways. Such data protection techniques can include, for example, data archiving techniques that cause data that is no longer actively used to be moved to a separate storage device or separate storage system for long-term retention, data backup techniques through which data stored in the storage system may be copied and stored in a distinct location to avoid data loss in the event of equipment failure or some other form of catastrophe with the storage system, data replication techniques through which data stored in the storage system is replicated to another storage system such that the data may be accessible via multiple storage systems, data snapshotting techniques through which the state of data within the storage system is captured at various points in time, data and database cloning techniques through which duplicate copies of data and databases may be created, and other data protection techniques. Through the use of such data protection techniques, business continuity and disaster recovery objectives may be met as a failure of the storage system may not result in the loss of data stored in the storage system.

[00123] The software resources 314 may also include software that is useful in implementing software-defined storage ('SDS'). In such an example, the software resources 314 may include one or more modules of computer program instructions that, when executed, are useful in policy-based provisioning and management of data storage that is independent of the underlying hardware. Such software resources 314 may be useful in implementing storage virtualization to separate the storage hardware from the software that manages the storage hardware.

[00124] The software resources 314 may also include software that is useful in facilitating and optimizing I/O operations that are directed to the storage resources 308 in the storage system 306. For example, the software resources 314 may include software modules that perform carry out various data reduction techniques such as, for example, data compression, data deduplication, and others. The software resources 314 may include software modules that intelligently group together I/O operations to facilitate better usage of the underlying storage resource 308, software modules that perform data migration operations to migrate from within a storage system, as well as software modules that perform other functions. Such software resources 314 may be embodied as one or more software containers or in many other ways.

[00125] Readers will appreciate that the various components depicted in Figure 3B may be grouped into one or more optimized computing packages as converged infrastructures. Such converged infrastructures may include pools of computers, storage and networking resources that can be shared by multiple applications and managed in a collective manner using policy- driven processes. Such converged infrastructures may minimize compatibility issues between various components within the storage system 306 while also reducing various costs associated with the establishment and operation of the storage system 306. Such converged infrastructures may be implemented with a converged infrastructure reference architecture, with standalone appliances, with a software driven hyper-converged approach, or in other ways.

[00126] Readers will appreciate that the storage system 306 depicted in Figure 3B may be useful for supporting various types of software applications. For example, the storage system 306 may be useful in supporting artificial intelligence applications, database applications, DevOps projects, electronic design automation tools, event-driven software applications, high performance computing applications, simulation applications, high-speed data capture and analysis applications, machine learning applications, media production applications, media serving applications, picture archiving and communication systems ('PACS') applications, software development applications, and many other types of applications by providing storage resources to such applications. [00127] Example methods and apparatus for evacuating blades in a storage array that includes a plurality of blades in accordance with the present invention are described with reference to the accompanying drawings, beginning with Figure 4. Figure 4 sets forth a diagram of a storage system in which blades may be evacuated from a storage array that includes a plurality of blades according to embodiments of the present disclosure. The storage system of Figure 4 includes a plurality of chassis (12, 16, 20, 24) mounted within a rack (10). The rack ( 10) depicted in Figure 4 may be embodied as a standardized frame or enclosure for mounting multiple equipment modules, such as each of the chassis (12, 16, 20, 24) depicted in Figure 4. The rack (10) may be embodied, for example, as a 19-inch rack that includes edges or ears that protrude on each side, thereby enabling a chassis (12, 16, 20, 24) or other module to be fastened to the rack (10) with screws or some other form of fastener. Readers will appreciate that while the storage system depicted in Figure 4 includes a plurality of chassis (12, 16, 20, 24) mounted within a single rack (10), in other embodiments the plurality of chassis (12, 16, 20, 24) may be distributed across multiple racks. For example, a first chassis in the storage system may be mounted within a first rack, a second chassis in the storage system may be mounted within a second rack, and so on.

[00128] The chassis (12, 16, 20, 24) depicted in Figure 4 may be embodied, for example, as passive elements that includes no logic. Each chassis (12, 16, 20, 24) may include a plurality of slots, where each slot is configured to receive a blade. Each chassis (12, 16, 20, 24) may also include a mechanism, such as a power distribution bus, that is utilized to provide power to each blade that is mounted within the chassis (12, 16, 20, 24). Each chassis (12, 16, 20, 24) may further include a communication mechanism, such as a communication bus, that enables communication between each blade that is mounted within the chassis ( 12, 16, 20, 24). The communication mechanism may be embodied, for example, as an Ethernet bus, Peripheral Component Interconnect Express ('PCIe') bus, InfiniBand bus, and so on. In some embodiments, each chassis (12, 16, 20, 24) may include at least two instances of both the power distribution mechanism and the communication mechanism, where each instance of the power distribution mechanism and each instance of the communication mechanism may be enabled or disabled independently.

[00129] Each chassis (12, 16, 20, 24) depicted in Figure 4 may also include one or more ports for receiving an external communication bus that enables communication between multiple chassis ( 12, 16, 20, 24), directly or through a switch, as well as communications between a chassis ( 12, 16, 20, 24) and an external client system. The external communication bus may use a technology such as Ethernet, InfiniBand, Fibre Channel, and so on. In some embodiments, the external communication bus may use different communication bus technologies for inter-chassis communication than is used for communication with an external client system. In embodiments where one or more switches are deployed, each switch may act as a translation between multiple protocols or technologies. When multiple chassis ( 12, 16, 20, 24) are connected to define a storage cluster, the storage cluster may be accessed by a client using either proprietary interfaces or standard interfaces such as network file system ('NFS'), common internet file system ('CIFS'), small computer system interface ('SCSI'), hypertext transfer protocol ('HTTP'), and so on. Translation from the client protocol may occur at the switch, external communication bus, or within each blade.

[00130] Each chassis (12, 16, 20, 24) depicted in Figure 4 houses fifteen blades (14, 18, 22, 26), although in other embodiments each chassis (12, 16, 20, 24) may house more or fewer blades. Each of the blades (14, 18, 22, 26) depicted in Figure 1 may be embodied, for example, as a computing device that includes one or more computer processors, dynamic random access memory ('DRAM'), flash memory, interfaces for one more communication busses, interfaces for one or more power distribution busses, cooling components, and so on. Although the blades (14, 18, 22, 26) will be described in more detail below, readers will appreciate that the blades (14, 18, 22, 26) depicted in Figure 1 may be embodied as different types of blades, such that the collective set of blades (14, 18, 22, 26) include heterogeneous members. Blades may be of different types as some blades (14, 18, 22, 26) may only provide processing resources to the overall storage system, some blades (14, 18, 22, 26) may only provide storage resources to the overall storage system, and some blades (14, 18, 22, 26) may provide both processing resources and storage resources to the overall storage system.

Furthermore, even the blades (14, 18, 22, 26) that are identical in type may be different in terms of the amount of storage resources that the blades (14, 18, 22, 26) provide to the overall storage system. For example, a first blade that only provides storage resources to the overall storage system may provide 8 TB of storage while a second blade that only provides storage resources to the overall storage system may provide 256 TB of storage. The blades (14, 18, 22, 26) that are identical in type may also be different in terms of the amount of processing resources that the blades ( 14, 18, 22, 26) provide to the overall storage system. For example, a first blade that only provides processing resources to the overall storage system may include more processors or more powerful processors than a second blade that only provides processing resources to the overall storage system. Readers will appreciate that other differences may also exist between two individual blades and that blade uniformity is not required according to embodiments described herein. [00131] Although not explicitly depicted in Figure 4, each chassis (12, 16, 20, 24) may include one or more modules, data communications bus, or other apparatus that is used to identify which type of blade is inserted into a particular slot of the chassis (12, 16, 20, 24). In such an example, a management module may be configured to request information from each blade in each chassis (12, 16, 20, 24) when each blade is powered on, when the blade is inserted into a chassis (12, 16, 20, 24), or at some other time. The information received by the management module can include, for example, a special purpose identifier maintained by the blade that identifies the type (e.g., storage blade, compute blade, hybrid blade) of blade that has been inserted into the chassis (12, 16, 20, 24). In an alternative embodiment, each blade (12, 16, 20, 24) may be configured to automatically provide such information to a management module as part of a registration process.

[00132] In the example depicted in Figure 4, the storage system may be initially configured by a management module that is executing remotely. The management module may be executing, for example, in a network switch control processor. Readers will appreciate that such a management module may be executing on any remote CPU and may be coupled to the storage system via one or more data communication networks. Alternatively, the management module may be executing locally as the management module may be executing on one or more of the blades (14, 18, 22, 26) in the storage system.

[00133] In the example depicted in Figure 4, one or more of the blades (14, 18, 22, 26) may be used for evacuating blades in a storage array by: detecting an occurrence of a blade evacuation event associated with one or more blades; iteratively until migration has completed for each of the blades associated with the blade evacuation event: selecting, in dependence upon a blade redundancy policy, one or more next blades to be evacuated from the storage array; migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the next blade; and migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades. One or more of the blades (14, 18, 22, 26) may be further used for evacuating blades in a storage array by: blocking write access to the blades associated with the blade evacuation event, copying, from the one or more next blades to one or more of the blades in the storage array that are not associated with the blade evacuation event, the data stored on the one or more next blades; initiating a garbage collection process on the one or more next blades, wherein the garbage collection process identifies valid data stored on the one or more next blades and invalid data stored on the one or more next blades; writing the valid data identified by the garbage collection process to the one or more blades in the storage array that are not associated with the blade evacuation event; rebuilding the data stored on the one or more next blades utilizing redundancy data stored in the storage array; identifying authorities executing on the one or more next blades; initiating, on one or more of the blades in the storage array that are not associated with the blade evacuation event, execution of the authorities; ceasing execution of the authorities on the one or more next blades; receiving a user-initiated request to evacuate the blades associated with the blade evacuation event; and erasing the data stored on the blades associated with the blade evacuation event; and presenting an indication that migration has completed for one or more of the blades associated with the blade evacuation event, as will be described in greater detail below. Readers will appreciate that while in some

embodiments one or more of the blades ( 14, 18, 22, 26) may be used for evacuating blades in a storage array by carrying out the steps listed above, in alternative embodiments, another apparatus that includes at least computer memory and a computer processor may be used for evacuating blades in a storage array by carrying out the steps listed above.

[00134] For further explanation, Figure 5 sets forth a diagram of a set of blades (32, 34, 36, 38) useful in evacuating blades in a storage array according to embodiments of the present disclosure. Although blades will be described in greater detail below, the blades (32, 34, 36, 38) depicted in Figure 5 may include compute resources (40, 42, 44), storage resources in the form of flash memory (60, 62, 64), storage resources in the form of non-volatile random access memory ('NVRAM') (70, 72, 74), or any combination thereof. In the example depicted in Figure 5, the blades (32, 34, 36, 38) are of differing types. For example, one blade (36) includes only compute resources (44), another blade (38) includes only storage resources, depicted here as flash (64) memory and NVRAM (74), and two of the blades (32, 34) include compute resources (40, 42) as well as storage resources in the form of flash (60, 62) memory and NVRAM (70, 72). In such of an example, the blade (36) that includes only compute resources (44) may be referred to as a compute blade, the blade (38) that includes only storage resources may be referred to as a storage blade, and the blades (32, 34) that include both compute resources (40, 42) and storage resources may be referred to as a hybrid blade.

[00135] The compute resources (40, 42, 44) depicted in Figure 5 may be embodied, for example, as one or more computer processors, as well as memory that is utilized by the computer processor but not included as part of general storage within the storage system. The compute resources (40, 42, 44) may be coupled for data communication with other blades and with external client systems, for example, via one or more data communication busses that are coupled to the compute resources (40, 42, 44) via one or more data communication adapters.

[00136] The flash memory (60, 62, 64) depicted in Figure 5 may be embodied, for example, as multiple flash dies which may be referred to as packages of flash dies or an array of flash dies. Such flash dies may be packaged in any number of ways, with a single die per package, multiple dies per package, in hybrid packages, as bare dies on a printed circuit board or other substrate, as encapsulated dies, and so on. Although not illustrated in Figure 5, an input output (I/O) port may be coupled to the flash dies and a direct memory access ('DMA') unit may also be coupled directly or indirectly to the flash dies. Such components may be implemented, for example, on a programmable logic device ('PLD') such as a field programmable gate array ('FPGA'). The flash memory (60, 62, 64) depicted in Figure 5 may be organized as pages of a predetermined size, blocks that include a predetermined number of pages, and so on.

[00137] The NVRAM (70, 72, 74) depicted in Figure 5 may be embodied, for example, as one or more non-volatile dual in-line memory modules ('NVDIMMs'), as one more DRAM dual in-line memory modules ('DIMMs') that receive primary power through a DIMM slot but are also attached to a backup power source such as a supercapacitor, and so on. The NVRAM (70, 72, 74) depicted in Figure 5 may be utilized as a memory buffer for temporarily storing data that will be written to flash memory (70, 72, 74), as writing data to the NVRAM (70, 72, 74) may be carried out more quickly than writing data to flash memory (70, 72, 74). In this way, the latency of write requests may be significantly improved relative to a system in which data is written directly to the flash memory (70, 72, 74).

[00138] In the example method depicted in Figure 5, a first blade (202) includes a first authority (168) that is executing on the compute resources (40) within the first blade (32) and a second blade (36) includes a second authority ( 168) that is executing on the compute resources (44) within the second blade (36). Each authority (168) represents a logical partition of control and may be embodied as a module of software executing on the compute resources (40, 42, 44) of a particular blade (32, 34, 36). Each authority (168) may be configured to control how and where data is stored in storage system. For example, authorities (168) may assist in determining which type of erasure coding scheme is applied to the data, authorities (168) may assist in determining where one or more portions of the data may be stored in the storage system, and so on. Each authority (168) may control a range of inode numbers, segment numbers, or other data identifiers which are assigned to data by a file system or some other entity.

[00139] Readers will appreciate that every piece of data and every piece of metadata stored in the storage system is owned by a particular authority (168). Each authority (168) may cause data that is owned by the authority (168) to be stored within storage that is located within the same blade whose computing resources are supporting the authority (168) or within storage that is located on some other blade. For example, the authority (168) that is executing on the compute resources (40) within a first blade (32) has caused data to be stored within a portion (52) of flash (60) and a portion (80) of NVRAM (70) that is physically located within the first blade (32), The authority (168) that is executing on the compute resources (40) within the first blade (32) has also caused data to be stored within a portion (54) of flash (62) on the second blade (34) in the storage system as well as a portion (58) of flash (64) and a portion (76) of NVRAM (74) on the fourth blade (38) in the storage system. Likewise, the authority (168) that is executing on the compute resources (44) within the third blade (32) has caused data to be stored within a portion (82) of NVRAM (70) that is physically located within the first blade (32), within a portion (56) of flash (62) within the second blade (34), within a portion (59) of flash (64) within the fourth blade (38), and within a portion (78) of NVRAM (74) within the fourth blade (38).

[00140] Readers will appreciate that many embodiments other than the embodiment depicted in Figure 5 are contemplated as it relates to the relationship between data, authorities, and system components. In some embodiments, every piece of data and every piece of metadata has redundancy in the storage system. In some embodiments, the owner of a particular piece of data or a particular piece of metadata may be a ward, with an authority being a group or set of wards. Likewise, in some embodiments there are redundant copies of authorities. In some embodiments, authorities have a relationship to blades and the storage resources contained therein. For example, each authority may cover a range of data segment numbers or other identifiers of the data and each authority may be assigned to a specific storage resource. Data may be stored in a segment according to some embodiments of the present disclosure, and such segments may be associated with a segment number which serves as indirection for a configuration of a Redundant Array of Independent Drives ('RAID') stripe. A segment may identify a set of storage resources and a local identifier into the set of storage resources that may contain data. In some embodiments, the local identifier may be an offset into a storage device and may be reused sequentially by multiple segments. In other embodiments the local identifier may be unique for a specific segment and never reused. The offsets in the storage device may be applied to locating data for writing to or reading from the storage device.

[00141] Readers will appreciate that if there is a change in where a particular segment of data is located (e.g., during a data move or a data reconstruction), the authority for that data segment should be consulted. In order to locate a particular piece of data, a hash value for a data segment may be calculated, an inode number may be applied, a data segment number may be applied, and so on. The output of such an operation can point to a storage resource for the particular piece of data. In some embodiments the operation described above may be carried out in two stages. The first stage maps an entity identifier (ID) such as a segment number, an inode number, an object ID, or directory number to an authority identifier. This mapping may include a calculation such as a hash or a bit mask. The second stage maps the authority identifier to a particular storage resource, which may be done through an explicit mapping. The operation may be repeatable, so that when the calculation is performed, the result of the calculation reliably points to a particular storage resource. The operation may take the set of reachable storage resources as input, and if the set of reachable storage resources changes, the optimal set changes. In some embodiments, a persisted value represents the current assignment and the calculated value represents the target assignment the cluster will attempt to reconfigure towards.

[00142] The compute resources (40, 42, 44) within the blades (202, 204, 206) may be tasked with breaking up data to be written to storage resources in the storage system. When data is to be written to a storage resource, the authority for that data is located as described above. When the segment ID for data is already determined, the request to write the data is forwarded to the blade that is hosting the authority, as determined using the segment ID. The computing resources on such a blade may be utilized to break up the data and transmit the data for writing to a storage resource, at which point the transmitted data may be written as a data stripe in accordance with an erasure coding scheme. In some embodiments, data is requested to be pulled and in other embodiments data is pushed. When compute resources (40, 42, 44) within the blades (32, 34, 36) are tasked with reassembling data read from storage resources in the storage system, the authority for the segment ID containing the data is located as described above.

[00143] The compute resources (40, 42, 44) within the blades 32, 34, 36) may also be tasked with reassembling data read from storage resources in the storage system. The compute resources (40, 42, 44) that support the authority that owns the data may request the data from the appropriate storage resource. In some embodiments, the data may be read from flash storage as a data stripe. The compute resources (40, 42, 44) that support the authority that owns the data may be utilized to reassemble the read data, including correcting any errors according to the appropriate erasure coding scheme, and forward the reassembled data to the network. In other embodiments, breaking up and reassembling data, or some portion thereof, may be performed by the storage resources themselves.

[00144] The preceding paragraphs discuss the concept of a segment. A segment may represent a logical container of data in accordance with some embodiments. A segment may be embodied, for example, as an address space between a medium address space and physical flash locations. Segments may also contain metadata that enables data redundancy to be restored (rewritten to different flash locations or devices) without the involvement of higher level software. In some embodiments, an internal format of a segment contains client data and medium mappings to determine the position of that data. Each data segment may be protected from memory and other failures, for example, by breaking the segment into a number of data and parity shards. The data and parity shards may be distributed by striping the shards across storage resources in accordance with an erasure coding scheme.

[00145] For further explanation, Figure 6 sets forth a diagram of a blade (303) useful in evacuating blades in a storage array according to embodiments of the present disclosure. As described above, the storage system may include storage blades, compute blades, hybrid blades, or any combination thereof. The example depicted in Figure 6 represents an embodiment of a hybrid blade as the blade (303) includes both compute resources and storage resources.

[00146] The compute resources in the blade (303) depicted in Figure 6 includes a host server (304) that includes a computer processor (307) coupled to memory (311) via a memory bus (308). The computer processor (306) depicted in Figure 6 may be embodied, for example, as a central processing unit ('CPU') or other form of electronic circuitry configured to execute computer program instructions. The computer processor (307) may utilize the memory (311) to store data or other information useful during the execution of computer program instructions by the computer processor (307). Such memory (311) may be embodied, for example, as DRAM that is utilized by the computer processor (307) to store information when the computer processor (307) is performing computational tasks such as creating and sending I/O operations to one of the storage units (313, 315), breaking up data, reassembling data, and other tasks.

[00147] In the example depicted in Figure 6, the computer processor (307) is coupled to two data communication links (333, 335). Such data communications links (333, 335) may be embodied, for example, as Ethernet links that are coupled to a data communication network via a network adapter. The computer processor (307) may receive input/output operations that are directed to the attached storage units (313, 315), such as requests to read data from the attached storage units (312, 314) or requests to write data to the attached storage units (312, 314).

[00148] The blade (303) depicted in Figure 6 also includes storage resources in the form of one or more storage units (313, 315). Each storage unit (313, 315) may include flash (329, 331) memory as well as other forms of memory (325, 327), such as the NVRAM discussed above. In the example depicted in Figure 6, the storage units (313, 315) may include integrated circuits such as a field-programmable gate array ('FPGA') (321, 323), microprocessors such as an Advanced RISC Machine ('ARM') microprocessor that are utilized to write data to and read data from the flash (329, 331) memory as well as the other forms of memory (325, 327) in the storage unit (313, 315), or any other form of computer processor. The FPGAs (321, 323) and the ARM (317, 319) microprocessors may, in some embodiments, perform operations other than strict memory accesses. For example, in some embodiments the FPGAs (321, 323) and the ARM (317, 319) microprocessors may break up data, reassemble data, and so on. In the example depicted in Figure 6, the computer processor (306) may access the storage units (313, 315) via a data communication bus (337) such as a PCIe bus.

[00149] Readers will appreciate that a compute blade may be similar to the blade (302) depicted in Figure 6 as the compute blade may include one or more host servers that are similar to the host server (305) depicted in Figure 6. Such a compute blade may be different than the blade (303) depicted in Figure 6, however, as the compute blade may lack the storage units (313, 315) depicted in Figure 6. Readers will further appreciate that a storage blade may be similar to the blade (303) depicted in Figure 6 as the storage blade may include one or more storage units that are similar to the storage units (313, 315) depicted in Figure 6. Such a storage blade may be different than the blade (303) depicted in Figure 6, however, as the storage blade may lack the host server (305) depicted in Figure 6. The example blade (303) depicted in Figure 6 is included only for explanatory purposes. In other embodiments, the blades may include additional processors, additional storage units, compute resources that are packaged in a different manner, storage resources that are packaged in a different manner, and so on.

[00150] For further explanation, Figure 7 sets forth a flow chart illustrating an example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The storage array (402) depicted in Figure 4 may be similar to the storage arrays described above, as the storage array (402) can include a plurality of blades (420, 422, 426, 428, 432, 434) that are mounted within chassis (418, 424, 430).

[00151] The example method depicted in Figure 7 can include detecting (404) an occurrence of a blade evacuation event associated with one or more blades. A blade evacuation event may indicate that the one or more blades (420, 422, 426, 428, 432, 434) should no longer be written to as the blades (420, 422, 426, 428, 432, 434) will ultimately be removed from the storage array (402). A blade evacuation event may also indicate that any workloads executing on the one or more blades (420, 422, 426, 428, 432, 434) should be relocated as the blades (420, 422, 426, 428, 432, 434) will ultimately be removed from the storage array (402). Before the blades (420, 422, 426, 428, 432, 434) are removed from the storage array (402), however, valid data on the blades (420, 422, 426, 428, 432, 434) and workloads executing on the blades (420, 422, 426, 428, 432, 434) should be relocated to other blades (420, 422, 426, 428, 432, 434) in the storage array (402). The blade evacuation event may be embodied, for example, as an event that is generated in response to a system administrator or other administrative entity indicating that the one or more blades (420, 422, 426, 428, 432, 434) are designated for removal from the storage array (402). The system administrator or other administrative entity may indicate that the one or more blades (420, 422, 426, 428, 432, 434) are designated for removal from the storage array (402), for example, through the use of a special purpose user interface (e.g., a GUI presented on a display screen) that presents an inventory of the blades (420, 422, 426, 428, 432, 434) that are included in the storage array (402) and that also allowed the user of the special purpose user interface to select one or more blades (420, 422, 426, 428, 432, 434) that are to be designated for removal from the storage array (402).

[00152] In the example method depicted in Figure 7, detecting (404) an occurrence of a blade evacuation event associated with one or more blades (420, 422, 426, 428, 432, 434) may be carried out by a special purpose module of computer program instructions that is executing on computer hardware within the storage array (402). Such a special purpose module of computer program instructions may be a standalone module or may be included within a larger module such as, for example, the blade evacuation module described below with reference to Figure 14. Such a special purpose module of computer program instructions may be executing, for example, on one or more computer processors within an array management server, on one or more computer processors within a storage array controller that is similar to the storage array controllers described above, or on other computer hardware within the storage array (402).

[00153] Readers will appreciate that one or more blades (420, 422, 426, 428, 432, 434) may be designated for removal from the storage array (402) for a variety of reasons. For example, the one or more blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may be relatively old blades that have a smaller storage capacity than relatively new blades that may be available as replacements for the relatively old blades. Alternatively, the blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may be relatively old blades that have higher access latencies and can't perform as many IOPS as relatively new blades that may be available as replacements for the relatively old blades. Likewise, the blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may be relatively old blades that have less processing power (e.g., fewer CPUs, slower CPUs, and so on) as relatively new blades that may be available as replacements for the relatively old blades. The one or more blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may be designated for removal from the storage array (402) as part of an upgrade to the storage array (402). Readers will appreciate that the blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may be designated for removal from the storage array (402) for other reasons, and readers will further appreciate that the blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may be designated for removal from the storage array (402) in spite of the fact that the blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) may still be properly functioning with no indication that a failure of the blades (420, 422, 426, 428, 432, 434) that are designated for removal from the storage array (402) is imminent.

[00154] The example method depicted in Figure 7 can also include selecting (406) one or more next blades to be evacuated from the storage array (402). The one or more next blades to be evacuated from the storage array (402) represent at least a portion of the blades that are associated with the blade evacuation event. The next blades to be evacuated from the storage array (402) are the next blades that will be evacuated from the storage array (402). Consider an example in which three blades (420, 428, 434) are associated with the blade evacuation event, indicating that the three blades (420, 428, 434) will eventually be removed from the storage array (402). In such an example, however, assume that the storage array (402) can only tolerate the loss of two blades at any given point in time without losing data stored in the storage array (402). Because the storage array (402) can only tolerate the loss of two blades at any given point in time without losing data stored in the storage array (402), it may be undesirable to effectively treat all three blades (420, 428, 434) as if they are unavailable. In addition, the amount of work required to migrate all of the data stored on all three blades (420, 428, 434) and the amount of work required to relocate all of the computational workloads executing on all three blades (420, 428, 434) at one time may negatively impair the ability of the storage array (402) to service I/O requests. As such, a staggered decommissioning of the three blades (420, 428, 434) associated with the blade evacuation event may be accomplished by selecting (406) a number of blades that will not cause data to be lost as the one or more next blades to be evacuated from the storage array (402). For example, a first blade (420) associated with the blade evacuation event may be selected (406) as the next blade to be evacuated from the storage array (402), a second blade (428) associated with the blade evacuation event may be selected (406) as the next blade to be evacuated from the storage array (402) only after the first blade (420) has been evacuated, and a third blade (434) associated with the blade evacuation event may be selected (406) as the next blade to be evacuated from the storage array (402) only after the second blade (428) has been evacuated.

[00155] Readers will appreciate that selecting (406) one or more next blades to be evacuated from the storage array (402) may be carried out in dependence upon a blade redundancy policy. The blade redundancy policy may include, for example, information describing the maximum number of blades that may be lost without resulting in a loss of data stored on the storage array (402). For example, some storage arrays may include a sufficient amount of redundancy data that two blades in the storage array (402) may be lost (e.g., by failing, by being removed from the storage array, and so on) without resulting in a loss of data stored on the storage array (402), as the data stored on the two lost blades may be rebuilt using redundancy data and data stored on blades in the storage array (402) that were not lost by performing RAID or RAID-like data redundancy operations. In such an example, the number of the one or more next blades selected to be evacuated from the storage array (402) may be less than the maximum number of blades that may be lost without resulting in the loss of data stored on the storage array (402). Readers will appreciate that in alternative embodiments, selecting (406) one or more next blades to be evacuated from the storage array (402) may be carried out in dependence upon other considerations such as, for example, an amount of processing resources that are to be allocated for relocating data stored on and processing workloads executing on blades that are associated with the blade evacuation event, an amount of I/O requests that are being directed to the storage array (402) as more resources may be dedicated to relocating data stored on and processing workloads executing on blades that are associated with the blade evacuation event during periods of low I/O activity, and so on.

[00156] The example method depicted in Figure 7 can also include migrating (408), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the one or more next blades. Migrating (408) the data stored on the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event may be carried out, for example, by writing the data stored on the one or more next blades to be evacuated from the storage array (402) to the one or more blades in the storage array (402) that are not associated with the blade evacuation event. Continuing with the example described above where three blades (420, 428, 434) are associated with the blade evacuation event and a first blade (420) associated with the blade evacuation event is selected (406) as the one or more next blades to be evacuated from the storage array (402), data stored on the first blade (420) may be migrated (408) to one or more of the blades (422, 426, 432) that are not associated with the blade evacuation event.

[00157] Readers will appreciate that if there is not sufficient space on the blades (422, 426, 432) that are not associated with the blade evacuation event to store the data stored on the first blade (420), migration (408) of the data may be aborted and the storage array (402) may be rolled back to its state prior to the occurrence of the blade evacuation event. In such an example, an array operating environment executing on a storage array controller may determine that insufficient space exists on the blades (422, 426, 432) that are not associated with the blade evacuation event if storing the data stored on the first blade (420) would cause the capacity utilization of the blades (422, 426, 432) that are not associated with the blade evacuation event to exceed a predetermined threshold.

[00158] Readers will appreciate that in some embodiments, only the valid data that is stored on the one or more next blades to be evacuated from the storage array (402) will be migrated (408) to the blades (422, 426, 432) that are not associated with the blade evacuation event, as invalid data does not need to be retained by migrating (408) such invalid data to the blades (422, 426, 432) that are not associated with the blade evacuation event. Consider an example in which a particular piece of data was stored at a first location within one of the next blades to be evacuated from the storage array (402). In such an example, assume that a request to modify the particular piece of data was subsequently received. In view of the fact that the storage devices within the blades (420, 422, 426, 428, 432, 434) may be embodied as an SSD, modifying the particular piece of data cannot be accomplished by simply overwriting the data as would occur in a hard disk drive. Instead, the modified version of the particular piece of data would be written to a second location (which may or may not be on the same blade) and the particular piece of data that was stored at the first location within one of the next blades to be evacuated from the storage array (402) would be marked as being invalid. As such, the one or more next blades to be evacuated from the storage array (402) may include some invalid data that has not yet been garbage collected, and such invalid data does not need to be retained by migrating (408) the invalid data to the blades (422, 426, 432) that are not associated with the blade evacuation event.

[00159] In an alternative embodiment, migrating (408) the data stored on the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event can include initiating a garbage collection process on the one or more next blades to be evacuated from the storage array (402). A garbage collection process may be embodied, for example, as a module of computer program instructions executing on computer hardware such as a computer processor or a microcontroller. The garbage collection process may be configured to reclaim memory that is occupied by data that is no longer in use. As described above, data that is no longer in use may be referred to herein as invalid data whereas data that is still in use may be referred to herein as valid data.

[00160] In the example method depicted in Figure 7, the garbage collection process may identify valid data stored on the one or more next blades to be evacuated from the storage array (402) and the garbage collection process can also identify invalid data on the one or more next blades to be evacuated from the storage array (402). The garbage collection process may identify valid data stored on the one or more next blades to be evacuated from the storage array (402) and the garbage collection process can also identify invalid data stored on the one or more next blades to be evacuated from the storage array (402), for example, by reading metadata that is associated with data stored in the storage array (402). Such metadata can include information that can be used to determine whether a particular piece of data is valid or invalid. The metadata may include such information as the result of steps carried out when data is written to the blades (420, 422, 426, 428, 432, 434).

[00161] Consider an example in which the storage devices within the blades (420, 422, 426, 428, 432, 434) are embodied as SSDs where data is written to the SSDs in 16 KB pages. Attached to each page in the SSD may be a small amount (e.g., 8 Bytes) of additional memory that is used to store metadata associated with the page. The SSDs may be configured to receive requests to write data from a storage array controller or other device, where the requests to write data include a virtual address that the SSD subsequently translates into a physical address. In such an example, the virtual-to-physical address translations may be stored by the SSD in a translation table that is maintained by the SSD. When the SSD receives a request to write data to a particular virtual address, the SSD may write the data to a first page that is associated with a first physical address and the SSD may also set a predetermined bit in the small amount of additional memory that is used to store metadata associated with the first page to a value indicating that the data contained therein is valid. If the SSD subsequently receives a second request to write data to the particular virtual address, the SSD may write the data to a second page that is described by a second physical address and also set a predetermined bit in the small amount of additional memory that is used to store metadata associated with the second page to a value indicating that the data contained therein is valid. In addition, the SSD may set the predetermined bit in the small amount of additional memory that is used to store metadata associated with the first page to a value indicating that the data contained therein is invalid, while also updating the translation table to map the particular virtual address to the second physical address. In such a way, the garbage collection process may scan the metadata associated with each page to determine whether the contents of each page are valid or invalid. Readers will appreciate that in other embodiments, metadata that is associated with data stored in the storage array (402) may be stored and maintained in other ways. In the example method depicted in Figure 4, migrating (408) the data stored on the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event can be carried out by writing the valid data identified by the garbage collection process to the one or more blades in the storage array (402) that are not associated with the blade evacuation event.

[00162] In another alternative embodiment, migrating (408) the data stored on the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event can include rebuilding the data stored on the one or more next blades to be evacuated from the storage array (402) using RAID or RAID-like operations. In such an example, at least a portion of the data stored on the blades associated with the blade evacuation event may be part of a data set that is striped across a plurality of blades. As such, redundancy data and/or data stored on blades other than the one or more next blades to be evacuated from the storage array (402) may be used to reconstruct the data stored on the one or more next blades to be evacuated from the storage array (402). In such an example, the reconstructed data may be stored on the one or more blades in the storage array (402) that are not associated with the blade evacuation event. [00163] The example method depicted in Figure 7 can also include migrating (410), from the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades. In the example method depicted in Figure 7, migrating (410) storage array computational workloads executing on the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event may be carried out, for example, by copying the source code for the computational workloads executing on the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event and initiating execution of such source code on the blades in the storage array (402) that are not associated with the blade evacuation event. In such an example, once all valid data stored on the one or more next blades to be evacuated from the storage array (402) has been migrated (408) to the blades in the storage array (402) that are not associated with the blade evacuation event and once all storage array computational workloads executing on the one or more next blades has been migrated (410) to one or more blades in the storage array (402) that are not associated with the blade evacuation event, the one or more next blades to be evacuated from the storage array (402) may be safely removed from the storage array (402). After the one or more next blades to be evacuated from the storage array (402) have been removed from the storage array (402), a new blade may be inserted in its place and the new blade may be added to the storage array (402) through a registration process that may be carried out, for example, by an array operating environment that is executing on a storage array (402). Such a registration process can be carried out by detecting the insertion of a blade into the storage array (402) and initializing the inserted blade. In such an example, detecting the insertion of a blade into the storage array (402) may be carried out through the use of software detection mechanisms or hardware components (e.g., presence detect lines) that detect the physical presence of a device and signal a storage array controller or similar device when a blade is inserted or removed from the storage array (402).

[00164] Readers will appreciate that in the example method depicted in Figure 7, the steps of selecting (402) one or more next blades to be evacuated from the storage array, migrating (408) data stored on one or more of the next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event, and migrating storage array computational workloads executing on one or more of the next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event may be performed iteratively until migration has completed for each of the blades associated with the blade evacuation event. Continuing with the example described above where three blades (420, 428, 434) are associated with the blade evacuation event and a first blade (420) associated with the blade evacuation event is selected (406) as the one or more next blades to be evacuated from the storage array (402), once all data stored on the first blade (420) has been migrated (408) and once all computational workloads executing on the first blade (420) have been migrated (410), the storage array (402) may continue by continuing the migration process for one or more of the other blades (428, 434) that are associated with the blade evacuation event. To that end, the storage array (402) may determine (412) whether migration has completed for each of the blades associated with the blade migration event. If the storage array (402) determines that migration has not (414) completed for each of the blades associated with the blade migration event, the storage array (402) may proceed by selecting (406) one or more next blades to be evacuated from the storage array (402). If the storage array (402) affirmatively (416) determines that migration has completed for each of the blades associated with the blade migration event, however, the storage array (402) may proceed by waiting to detect (404) an occurrence of a new blade evacuation event associated with one or more blades.

[00165] For further explanation, Figure 8 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The example method depicted in Figure 5 is similar to the example method depicted in Figure 4, as the example method depicted in Figure 5 also includes detecting (404) an occurrence of a blade evacuation event associated with one or more blades, selecting (406) one or more next blades to be evacuated from the storage array (402), migrating (408), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the next blade, and migrating (410), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades.

[00166] The example method depicted in Figure 8 also includes blocking (502) write access to the blades associated with the blade evacuation event. Blocking (502) write access to the blades associated with the blade evacuation event may be carried out, for example, by each of the storage array controllers in the storage array (402) ceasing to issue write operations to the blades associated with the blade evacuation event. In such an example, each storage array controller may maintain a list or other data structure that identifies all blades in the storage array (402) that should not be utilized to service write operations. Because the storage array controller is responsible for directing all access requests to the blades (420, 422, 426, 428, 432, 434) in the storage array (402), the storage array controller may ultimately enforce a policy to block (502) all write access to the blades associated with the blade evacuation event. In an alternative embodiment, blocking (502) write access to the blades associated with the blade evacuation event may be carried out, for example, by each of the authorities (or any other entity that initiates write operations) ceasing to issue write operations to the blades associated with the blade evacuation event. In such an example, each of the authorities (or any other entity that initiates write operations) may maintain a list or other data structure that identifies all blades in the storage array (402) that should not be utilized to service write operations. In yet an alternative embodiment, the blades associated with the blade evacuation event may respond to a request to write data with an error message or other indication that the request was not serviced, such that blocking (502) write access to the blades associated with the blade evacuation event may be carried out by the blades that are associated with the blade evacuation event themselves. In such an example, the blades that are associated with the blade evacuation event are essentially placed in a read-only mode as read requests may continue to be serviced until the blades are fully decommissioned and removed from the storage array (402).

[00167] The example method depicted in Figure 8 also includes reducing (504) write access to the blades associated with the blade evacuation event. In the example method depicted in Figure 5, reducing (504) write access to the blades associated with the blade evacuation event may be carried out, for example, by only allowing the blades that are associated with the blade evacuation event to service a predetermined number of write requests using the mechanisms described in the preceding paragraph. Readers will appreciate that in the examples described above, where write access to the blades associated with the blade evacuation event is reduced (504) or blocked (502), the presence of deduplicated data on the blades associated with the blade evacuation event may be treated as a special case. Data deduplication is a data compression technique whereby duplicate copies of repeating data are eliminated. Through the use of data deduplication techniques, a unique chunk of data (e.g., the master copy) may be stored once in the storage array (402) and all additional occurrences of the chunk of data are replaced with a small reference that points to the stored chunk. The deduplicated data on the blades associated with the blade evacuation event may therefore be embodied, for example, as a piece of data that is stored on the blades associated with the blade evacuation event, where the piece of data is pointed to by other occurrences of identical data in the storage array (402). The presence of deduplicated data on the blades associated with the blade evacuation event may be handled, for example, by allowing read-write access to the deduplicated data while enabling read-only access to (or blocking write access to) the remaining portions of the blades associated with the blade evacuation event (e.g., those portions that do not contain deduplicated data). Alternatively, the deduplicated data may be migrated to another blade in the storage array and all references to the deduplicated data may be updated to point to the new location where the deduplicated data is stored. Furthermore, if a write request is received that would normally be deduplicated due to the presence of identical data on the blades associated with the blade evacuation event, such a write request may be serviced by a blade that is not associated with the blade evacuation event, the metadata associated with deduplicated instances of such data may be updated to point to the newly written instance of the data, and the instance of the data that is stored on the blade that is associated with the blade evacuation event may be invalidated.

[00168] In the example method depicted in Figure 8, migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event can include copying (506), from the one or more next blades to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event, the data stored on the one or more next blades. Copying (506) the data stored on the one or more next blades to be evacuated from the storage array (402) may be carried out, for example, by a storage array controller or other device reading the data stored on the one or more next blades to be evacuated from the storage array (402) and the storage array controller or other device writing such data to one or more of the blades that are not associated with the blade evacuation event. In an alternative embodiment, the one or more next blades to be evacuated from the storage array (402) themselves may be configured to support a copy operation that takes an identification of a source and an identification of a target as operands. In such an example, the operands may be specified as a range of physical addresses, a range of virtual addresses, a base address and an indication of the size of the data that is to be copied, an identification of a logical grouping of data such as a volume, and so on.

[00169] In the example method depicted in Figure 8, migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event can alternatively include rebuilding (508) the data stored on the one or more next blades utilizing redundancy data stored in the storage array (402). Rebuilding (508) the data stored on the one or more next blades utilizing redundancy data stored in the storage array (402) may be carried out through the use of RAID or RAID-like operations. In such an example, at least a portion of the data stored on the blades associated with the blade evacuation event may be part of a data set that is striped across a plurality of blades. As such, redundancy data and/or data stored on blades other than the one or more next blades to be evacuated from the storage array (402) may be used to reconstruct the data stored on the one or more next blades to be evacuated from the storage array (402). In such an example, the reconstructed data may be stored on the one or more blades in the storage array (402) that are not associated with the blade evacuation event.

[00170] Readers will appreciate that because migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) may be carried out by rebuilding (508) the data stored on the one or more next blades utilizing redundancy data stored in the storage array (402), the evacuation process may be terminated early in some instances (at least relative to a system that does not include redundancy data). Consider an example in which three blades (420, 426, 432) are targeted for removal from the storage array (402) as a blade evacuation event that is associated with the three blades (420, 426, 432) is detected (404). In such an example, further assume that the storage array (402) includes a sufficient amount of redundancy data such that two blades may be lost without resulting in the loss of data. Further assume that all data that is stored on one of the blades (420) has been successfully migrated. In such an example, because two blades may be lost without resulting in the loss of data, it may be possible to terminate the evacuation process early, remove the other two blades (426, 432) that are associated with the blade evacuation event, and install two new blades, as the data that was previously stored on the other two blades (426, 432) that are associated with the blade evacuation event may be rebuilt only the newly inserted new blades. As such, so long as the computational workloads that are executing on the other two blades (426, 432) have been successfully migrated, no content on the other two blades (426, 432) will be lost. Readers will appreciate that deciding whether to terminate the evacuation process early may therefore be carried out by: identifying one or more blades that are associated with the blade evacuation event and whose content has not been fully migrated; determining whether all computational workloads have been migrated away from the blades whose content has not been fully migrated; determining whether the data stored on the blades whose content has not been fully migrated can be rebuilt; and responsive to determining that the data stored on the blades whose content has not been fully migrated can be rebuilt, terminating the migration process. [00171] In the example method depicted in Figure 8, migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event can alternatively include initiating (510) a garbage collection process on the one or more next blades. A garbage collection process may be embodied, for example, as a module of computer program instructions executing on computer hardware such as a computer processor or a

microcontroller. The garbage collection process may be configured to reclaim memory that is occupied by data that is no longer in use.

[00172] In the example method depicted in Figure 8, the garbage collection process may identify valid data stored on the one or more next blades and invalid data stored on the one or more next blades. As described above, data that is no longer in use may be referred to herein as invalid data whereas data that is still in use may be referred to herein as valid data. The garbage collection process may identify valid data stored on the one or more next blades to be evacuated from the storage array (402) and the garbage collection process can also identify invalid data on the one or more next blades to be evacuated from the storage array (402). The garbage collection process may identify valid data stored on the one or more next blades to be evacuated from the storage array (402) and the garbage collection process can also identify invalid data stored on the one or more next blades to be evacuated from the storage array (402), for example, by reading metadata that is associated with data stored in the storage array (402). Such metadata can include information that can be used to determine whether a particular piece of data is valid or invalid. The metadata may include such information as the result of steps carried out when data is written to the blades (420, 422, 426, 428, 432, 434).

[00173] Consider an example in which the storage devices within the blades (420, 422, 426, 428, 432, 434) are embodied as SSDs where data is written to the SSDs in 16 KB pages. Attached to each page in the SSD may be a small amount (e.g., 8 Bytes) of additional memory that is used to store metadata associated with the page. The SSDs may be configured to receive requests to write data from a storage array controller or other device, where the requests to write data include a virtual address that the SSD subsequently translates into a physical address. In such an example, the virtual-to-physical address translations may be stored by the SSD in a translation table that is maintained by the SSD. When the SSD receives a request to write data to a particular virtual address, the SSD may write the data to a first page that is associated with a first physical address and the SSD may also set a predetermined bit in the small amount of additional memory that is used to store metadata associated with the first page to a value indicating that the data contained therein is valid. If the SSD subsequently receives a second request to write data to the particular virtual address, the SSD may write the data to a second page that is described by a second physical address and also set a predetermined bit in the small amount of additional memory that is used to store metadata associated with the second page to a value indicating that the data contained therein is valid. In addition, the SSD may set the predetermined bit in the small amount of additional memory that is used to store metadata associated with the first page to a value indicating that the data contained therein is invalid, while also updating the translation table to map the particular virtual address to the second physical address. In such a way, the garbage collection process may scan the metadata associated with each page to determine whether the contents of each page are valid or invalid. Readers will appreciate that in other embodiments, metadata that is associated with data stored in the storage array (402) may be stored and maintained in other ways.

[00174] In the example method depicted in Figure 8, migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event can also include writing (512) the valid data identified by the garbage collection process to the one or more blades in the storage array that are not associated with the blade evacuation event. Writing (512) the valid data identified by the garbage collection process to the one or more blades in the storage array that are not associated with the blade evacuation event may be carried out, for example, by combining individual chunks of valid data that were identified by the garbage collection process into one or more blocks of valid data of a predetermined size and writing the one or more blocks of valid data of a predetermined size to one or more of the blades in the storage array that are not associated with the blade evacuation event.

[00175] Consider an example in which the storage devices within the blades (420, 422, 426, 428, 432, 434) are embodied as SSDs, where data can be written to the SSDs in 16 KB pages but data can only be erased from the SSDs by erasing an entire memory block that includes 256 16 KB pages. In such an example, individual chunks of valid data that were identified by the garbage collection process may be combined into 4 MB blocks (the size of a memory block in the SSD) and written to the SSD into a single memory block in the SSD. Readers will appreciate that by combining individual chunks of valid data that were identified by the garbage collection process into 4 MB blocks and writing the 4 MB blocks to a single memory block in the SSD, the single memory block in the SSD will only contain valid data. Writing the individual chunks of valid data that were identified by the garbage collection process into memory blocks on the SSD that include no invalid data can improve system performance relative to writing the individual chunks of valid data that were identified by the garbage collection process into a memory block in the SSD that already contains invalid data. System performance can be improved in such an example because the memory blocks in the SSD that already contain invalid data are ripe for garbage collection, meaning that any valid data contained in the memory blocks in the SSD that contain invalid data will need to be relocated when a garbage collection process examines the memory block in the SSD that already contains invalid data. Relocating data through a garbage collection process utilizes system resources as valid data contained in a memory block that is to be garbage collected must be written to a new location (additional writes) and the memory block that is to be garbage collected must also be erased (additional erase operations). As such, system performance may be improved by reducing the amount of memory blocks that need to be garbage collected and reducing the amount of data that needs to be relocated.

[00176] Readers will appreciate that the preceding paragraph describes only example of combining individual chunks of valid data that were identified by the garbage collection process into one or more blocks of valid data of a predetermined size and writing the one or more blocks of valid data of a predetermined size to one or more of the blades in the storage array that are not associated with the blade evacuation event. Other examples exist and other policies may be put in place in pursuit of other objectives.

[00177] Although the preceding paragraphs discuss embodiments where migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) includes copying (506) the data stored on the one or more next blades, or rebuilding (508) the data stored on the one or more next blades utilizing redundancy data stored in the storage array (402), or initiating (510) a garbage collection process on the one or more next blades, readers will appreciate that a combination of such techniques may be applied to migrate (408) the data that is stored on the one or more next blades to be evacuated from the storage array (402). In addition, one or more policies may be implemented to determine the extent to which each of the techniques will be applied to migrate (408) the data that is stored on the one or more next blades to be evacuated from the storage array (402). Such a policy may specify, for example, that migrating (408) data stored on the one or more next blades to be evacuated from the storage array (402) should be carried out primarily by rebuilding (508) the data stored on the one or more next blades utilizing redundancy data stored in the storage array (402) in situations where there is a relatively small amount of garbage on a particular blade, as rebuilding the data may be more efficient than executing a garbage collection process that will ultimately collect very little garbage. Readers will appreciate that many other policies may be enforced and that such policies may be applied to determine how data will be migrated from each blade, to determine how data will be migrated from different portions of storage on each blade, and so on.

[00178] For further explanation, Figure 9 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The example method depicted in Figure 6 is similar to the example method depicted in Figure 4, as the example method depicted in Figure 6 also includes detecting (404) an occurrence of a blade evacuation event associated with one or more blades, selecting (406) one or more next blades to be evacuated from the storage array (402), migrating (408), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the next blade, and migrating (410), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades.

[00179] In the example method depicted in Figure 9, migrating (410) storage array computational workloads executing on the one or more next blades can include identifying (602) authorities executing on the one or more next blades to be evacuated from the storage array (402). In the example method depicted in Figure 6, authorities such as the authorities described above, may represent one form of computational workloads that are to be migrated (410). In such an example, each authority executing on a blade may register with the blade or the blade may otherwise have knowledge that the authority is executing on compute resources in the blade. As such, identifying (602) authorities executing on the one or more next blades to be evacuated from the storage array (402) may be carried out, for example, by identifying information such as an authority ID for each authority that is executing on the one or more next blades to be evacuated from the storage array (402).

[00180] In the example method depicted in Figure 9, migrating (410) storage array computational workloads executing on the one or more next blades can also include initiating (604), on one or more of the blades in the storage array (402) that are not associated with the blade evacuation event, execution of the authorities identified (602) in the preceding paragraph. Initiating (604) execution of the authorities identified (602) in the preceding paragraph on one or more of the blades in the storage array (402) that are not associated with the blade evacuation event may be carried out, for example, by copying source code for the authority to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event and initiating execution of such source code. In the example method depicted in Figure 6, migrating (410) storage array computational workloads executing on the one or more next blades can also include ceasing (606) execution of the authorities on the one or more next blades to be evacuated from the storage array (402).

[00181] For further explanation, Figure 10 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The example method depicted in Figure 10 is similar to the example method depicted in Figure 4, as the example method depicted in Figure 10 also includes detecting (404) an occurrence of a blade evacuation event associated with one or more blades, selecting (406) one or more next blades to be evacuated from the storage array (402), migrating (408), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the next blade, and migrating (410), from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades.

[00182] In the example method depicted in Figure 10, detecting (404) an occurrence of a blade evacuation event associated with one or more blades can include receiving (702) a user- initiated request to evacuate the blades associated with the blade evacuation event. The user- initiated request to evacuate the blades associated with the blade evacuation event may be received (702), for example, through the use of a command-line interface, through the use of a user interface (e.g., a GUI presented on a display screen) that presents an inventory of the blades that are included in the storage array (402) and that also allows the user of the user interface to select one or more blades that are to be designated for removal from the storage array (402), of through the use of some other interface. Readers will appreciate that a user- initiated request to evacuate the blades associated with the blade evacuation event may be received (702) in other ways in other embodiments. In an alternative embodiment, detecting (404) an occurrence of a blade evacuation event associated with one or more blades can include receiving a system-initiated request to evacuate the blades associated with the blade evacuation event. Such a system-initiated request to evacuate the blades associated with the blade evacuation event may be generated, for example, as part of a scheduled upgrade, in response to blades reaching a predetermined age, in response to blade exhibiting poor performance, and for other reasons. [00183] The example method depicted in Figure 10 also includes erasing (704) the data stored on the blades associated with the blade evacuation event. In such an example, erasing (704) the data stored on the blades associated with the blade evacuation event may be carried out as a security measure to ensure that once the blade is removed from the storage array (402), the data contained on such a blade will not fall into the wrong hands.

[00184] The example method depicted in Figure 10 also includes presenting (706) an indication that migration has completed for one or more of the blades associated with the blade evacuation event. In the example method depicted in Figure 10, the indication that migration has completed for one or more of the blades associated with the blade evacuation event may be embodied, for example, as a message that appears on a GUI, as a message that is sent to a designated user such as a system administrator, through the use of a light on a particular blade that may be illuminated once migration has completed, and so on.

[00185] Readers will appreciate that although erasing (704) the data stored on the blades associated with the blade evacuation event and presenting (706) an indication that migration has completed for one or more of the blades associated with the blade evacuation event are illustrated in Figure 10 as occurring after the storage array (402) affirmatively (416) determines that migration has completed for each of the blades associated with the blade migration event. In alternative embodiments, however, erasing (704) the data stored on the blades associated with the blade evacuation event and/or presenting (706) an indication that migration has completed for one or more of the blades associated with the blade evacuation event may occur on a blade by blade basis, after the storage array (402) determines that migration has not (414) completed for each of the blades associated with the blade migration event.

[00186] For further explanation, Figure 1 1 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The example method depicted in Figure 8 is similar to the example method depicted in Figure 7, as the example method depicted in Figure 8 also includes detecting (404) an occurrence of a blade evacuation event associated with one or more blades.

[00187] In the example method depicted in Figure 1 1, detecting (404) an occurrence of a blade evacuation event associated with one or more blades can include receiving (802) a system-initiated request to evacuate the blades associated with the blade evacuation event. The system-initiated request to evacuate the blades associated with the blade evacuation event may be generated, for example, by a system management module or other form of computer program instructions executing on computer hardware such as a computer processor. Such a system-initiated request to evacuate the blades associated with the blade evacuation event may be generated, for example, as part of a scheduled upgrade, in response to blades reaching a predetermined age, in response to blade exhibiting poor performance, and for other reasons.

[00188] The example method depicted in Figure 1 1 also includes placing (804) the blades associated with the blade evacuation event in a read-only mode. Placing (804) the blades associated with the blade evacuation event in a read-only mode may be carried out, for example, by configuring a setting within the blades associated with the blade evacuation event that will cause the blades to reject any incoming write requests, by notifying all entities that issue write requests that write requests are not to be directed to the blades that are associated with the blade evacuation event, and so on. In such an example, the blades that are associated with the blade evacuation event may continue to service read requests directed to the blades, but the blades that are associated with the blade evacuation event may cease to service write requests as any valid data stored on such blades will ultimately be migrated to blades in the storage array (402) that are not associated with the blade evacuation event.

[00189] The example method depicted in Figure 1 1 also includes selecting (806) one or more next blades to be evacuated from the storage array (402). Selecting (806) one or more next blades to be evacuated from the storage array (402) may be carried out in dependence upon a variety of considerations. For example, the number of I/O requests that the storage array (402) must be able to service as specified in a service level agreement may be taken into consideration when selecting (806) one or more next blades to be evacuated from the storage array (402). Consider an example in which three blades (420, 428, 434) are associated with the blade evacuation event, indicating that the three blades (420, 428, 434) will eventually be removed from the storage array (402). In such an example, however, assume that the storage array (402) can only tolerate the loss of two blades at any given point in time without violating the terms of the service level agreement, as the loss of more than two blades at any given time will prevent the storage array (402) from servicing the number of I/O requests that the storage array (402) must be able to service as specified in a service level agreement. Because the storage array (402) can only tolerate the loss of two blades at any given point in time without violating the terms of the service level agreement, it may be undesirable to effectively treat all three blades (420, 428, 434) as if they are unavailable. As such, a staggered decommissioning of the three blades (420, 428, 434) associated with the blade evacuation event may be necessary to avoid the violation of the service level agreement. A staggered decommissioning of the three blades (420, 428, 434) associated with the blade evacuation event may be carried out, for example, by selecting (806) a first blade (420) associated with the blade evacuation event as the next blade to be evacuated from the storage array (402), selecting (806) a second blade (428) associated with the blade evacuation event as the next blade to be evacuated from the storage array (402) only after the first blade (420) has been evacuated, and selecting (806) a third blade (434) associated with the blade evacuation event as the next blade to be evacuated from the storage array (402) only after the second blade (428) has been evacuated. Readers will appreciate that in other embodiments, additional or different factors may be taken into consideration when selecting (806) one or more next blades to be evacuated from the storage array (402). For example, selecting (806) one or more next blades to be evacuated from the storage array (402) may be carried out in dependence upon a blade redundancy policy, as described above. Readers will appreciate that in other embodiments, selecting (806) one or more next blades to be evacuated from the storage array (402) may be carried out in dependence upon other considerations such as, for example, an amount of processing resources that are to be allocated for relocating data stored on and processing workloads executing on blades that are associated with the blade evacuation event, an amount of I/O requests that are being directed to the storage array (402) as more resources may be dedicated to relocating data stored on and processing workloads executing on blades that are associated with the blade evacuation event during periods of low I/O activity, and so on.

[00190] The example method depicted in Figure 11 also includes migrating (808), from the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event, all array-related content. The array-related content can include, for example, data that is stored on the storage array (402), computational workloads that are executing on a blade (420, 422, 426, 428, 432, 434) in the storage array (402), and so on. In the example method depicted in Figure 8, migrating (808), from the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event, all array-related content can therefore include migrating (810) data stored on the one or more next blades to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event. Migrating (808), from the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event, all array-related content can alternatively include migrating (812) all storage array computational workloads executing on the one or more next blades to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event.

[00191] Readers will appreciate that, as described above, blades in the storage array (402) may be embodied as storage blades, compute blades, and hybrid blades. When a storage blade is associated with a blade evacuation event, migrating (808) all array-related content from the storage blade may include migrating (810) data stored on the storage blade to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event. When a compute blade is associated with a blade evacuation event, however, migrating (808) all array-related content from the compute blade may include migrating (812) all storage array computational workloads executing on the compute blade to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event. Likewise, when a hybrid blade is associated with a blade evacuation event, migrating (808) all array-related content from the hybrid blade may include migrating (810) data stored on the hybrid blade to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event, as well as migrating (812) all storage array computational workloads executing on the hybrid blade to one or more of the blades in the storage array (402) that are not associated with the blade evacuation event.

[00192] In the example method depicted in Figure 1 1, migrating (808), from the one or more next blades to one or more blades in the storage array (402) that are not associated with the blade evacuation event, all array-related content may be carried out in dependence upon a migration policy. Such a migration policy can place include information that is used to place limitations or restrictions on the migration process. Such a migration policy may specify, for example, a maximum amount of time that may allocated for migrating array-related content, a maximum amount of resources that may be dedicated to migrating array-related content, criteria for selecting which blades that are not associated with a blade evacuation event should be selected for receiving array-related content from blades that are associated with the blade evacuation event, and so on.

[00193] In the example method depicted in Figure 1 1, the migration policy may also specify one or more performance criteria for the storage array (402). The one or more performance criteria may include information that identifies performance levels that the storage array (402) must maintain and therefore may represent a limitation on the amount of storage array (402) resources that may be utilized for migrating (808) all array-related content from the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event. Such performance criteria may include, for example, an amount of IOPS that the storage array (402) must be able to service, an amount of network bandwidth that should be reserved for servicing I/O requests directed to the storage array, an amount of processing cycles that the storage array (402) must make available for computational workloads that are executing on the storage array (402), and so on. In such an example, the extent to which all array-related content is migrated (808) may be limited by such performance criteria for the storage array (402), as sufficient resources should be reserved for servicing I/O requests directed to the storage array (or otherwise delivering the required level of service) rather than dedicating such resources to the migration of all array-related content from the one or more next blades that are to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event.

[00194] The example method depicted in Figure 1 1 also includes presenting (814) an indication that migration has completed for one or more of the next blades to be evacuated from the storage array (402). In the example method depicted in Figure 10, the indication that migration has completed for one or more of the next blades to be evacuated from the storage array (402) may be embodied, for example, as a message that appears on a GUI, as a message that is sent to a designated user such as a system administrator, through the use of a light on a particular blade that may be illuminated once migration has completed, and so on.

[00195] In the example method depicted in Figure 8, the storage array includes a plurality of chassis (418, 424, 430), where each chassis (418, 424, 430) is configured to support a plurality of blades (420, 422, 426, 428, 432, 434). As such, at least a portion of the array- related content may be migrated (808) from a blade mounted in a first chassis to a blade mounted in a second chassis. For example, in the process of migrating (808) all array-related content from the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event, data stored on a blade in a first chassis may be migrated to one or more blades in a second chassis, computational workloads executing on a blade in a first chassis may be migrated to one or more blades in a second chassis, and so on.

[00196] For further explanation, Figure 12 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The example method depicted in Figure 12 is similar to the example methods described above, as the example method depicted in Figure 12 also includes detecting (404) an occurrence of a blade evacuation event associated with one or more blades, selecting (806) one or more next blades to be evacuated from the storage array (402), migrating (808) all array-related content from the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event.

[00197] In the example method depicted in Figure 12, migrating (808) all array-related content from the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event can include migrating (902) all array-related content (906) from the one or more next blades to be evacuated from the storage array (402) to a system (908) that is external to the storage array (402). The system (908) that is external to the storage array (402) may be embodied, for example, as a cloud-based system that contains storage resources and processing resources that are available for use by the storage array (402), as another storage array that is available to temporarily store data and support computational workloads on behalf of the storage array (402), and so on. In such an example, array-related content (906) may be sent to the system (908) that is external to the storage array (402) via one or more data communications messages exchanged over a data communications network between the storage array (402) and the system (908) that is external to the storage array (402), array- related content (906) may be sent to the system (908) that is external to the storage array (402) via one or more remote direct memory access ('RDMA') interfaces between the storage array (402) and the system (908) that is external to the storage array (402), and in many other ways. Readers will appreciate that by migrating (902) all array-related content (906) from the one or more next blades to be evacuated from the storage array (402) to a system (908) that is external to the storage array (402), fewer resources within the storage array (402) may be consumed during the migration process, thereby enabling resources within the storage array (402) to remain available for supporting other storage array tasks such as servicing I/O operations.

[00198] In the example method depicted in Figure 12, migrating (808) all array-related content from the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event can also include placing (904) all array-related content (906) received from the system (908) that is external to the storage array (402) on the one or more blades in the storage array (402) that are not associated with the blade evacuation event. The array-related content (906) may be received from the system (908) that is external to the storage array (402) at some point in time after the array-related content (906) was migrated (902) from the one or more next blades to be evacuated from the storage array (402) to the system (908) that is external to the storage array (402). As such, in between the time that the array-related content (906) was migrated (902) from the one or more next blades to be evacuated from the storage array (402) to the system (908) that is external to the storage array (402) and the time that the array-related content (906) was received from the system (908) that is external to the storage array (402), one or more of the blades that are associated with the evacuation event may be removed and replacement blades may be inserted. In such a way, the system (908) that is external to the storage array (402) may be used as resources that temporarily support the migration process. The array-related content (906) may be received from the system (908) that is external to the storage array (402), for example, via one or more data communications messages exchanged over a data communications network between the storage array (402) and the system (908) that is external to the storage array (402), via one or more RDMA interfaces between the storage array (402) and the system (908) that is external to the storage array (402), and in many other ways.

[00199] For further explanation, Figure 13 sets forth a flow chart illustrating an additional example method of evacuating blades in a storage array (402) that includes a plurality of blades (420, 422, 426, 428, 432, 434) according to embodiments of the present disclosure. The example method depicted in Figure 13 is similar to the example methods described above, as the example method depicted in Figure 10 also includes detecting (404) an occurrence of a blade evacuation event associated with one or more blades, selecting (806) one or more next blades to be evacuated from the storage array (402), migrating (808) all array-related content from the one or more next blades to be evacuated from the storage array (402) to one or more blades in the storage array (402) that are not associated with the blade evacuation event.

[00200] The example method depicted in Figure 13 also includes determining (1002) whether migration of one or more blades associated with the blade evacuation event can proceed. Determining (1002) whether migration of array-related content on one or more blades associated with the blade evacuation event can proceed may be carried out, for example, by determining whether migration of array-related content can proceed in a way that satisfies a migration policy, by determining whether a required level of system performance can be maintained when performing a migration of array-related content on one or more blades associated with the blade evacuation event, by determining whether a sufficient amount of available storage and compute resources exist on blades that are not associated with the blade evacuation event to perform a migration of array-related content on one or more blades associated with the blade evacuation event, and so on. If it is affirmatively (1004) determined that migration of array-related content on one or more blades associated with the blade evacuation event can proceed, the storage array (402) may proceed by selecting (806) one or more next blades to be evacuated from the storage array (402).

[00201] In the example method depicted in Figure 13, if it is determined that migration of array-related content on one or more blades associated with the blade evacuation event cannot (1006) proceed, the storage array (402) may wait to proceed until the storage array detects (1008) a system configuration change. Detecting (1008) a system configuration change may be carried out, for example, by detecting that a new blade has been inserted into the storage array (402), by detecting that a previously unavailable blade in the storage array (402) has become available, by detecting that the amount of available storage resources or available compute resources in the storage array (402) has changed, by detecting that one or more system configuration settings for the storage array (402) has changed, and so on. In such an example, the system configuration changes may cause the storage array (402) to be able to proceed with the migration of array-related content on one or more blades associated with the blade evacuation event. As such, once a system configuration change has been detected (1008), the storage array (402) may proceed by again determining (1002) whether migration of one or more blades associated with the blade evacuation event can proceed.

[00202] Readers will appreciate that in addition to making determinations as to whether migration of array-related content on one or more blades associated with the blade evacuation event can (1004) or cannot (1006) proceed, in alternative embodiments, the migration of array-related content on one or more blades associated with the blade evacuation event may be paused and resumed for a variety of reasons. For example, the migration of array-related content on one or more blades associated with the blade evacuation event may be paused during periods of relatively heavy system utilization so that the storage array (402) can use its resources to service I/O requests rather than migrating array-related content away from the blades that are associated with the blade evacuation event. In such an example, the migration of array-related content on the blades that are associated with the blade evacuation event may be resumed during periods of relatively light system utilization, as the storage array (402) may have resources that can be used to migrate array-related content away from the blades that are associated with the blade evacuation event without degrading system performance to an unacceptable level. Readers will appreciate that the migration of array-related content away from the blades that are associated with the blade evacuation event may be paused and resumed for a variety of other reasons, and that pausing and resuming array-related content away from the blades that are associated with the blade evacuation event may occur in response to a user request, at the behest of system management software, or any combination thereof.

[00203] For further explanation, Figure 14 sets forth a block diagram of automated computing machinery comprising an example computer (1152) useful in evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure. The computer (1152) of Figure 11 includes at least one computer processor (1156) or "CPU" as well as random access memory ("RAM") (1168) which is connected through a high speed memory bus (1166) and bus adapter (1158) to processor (1156) and to other components of the computer (1152). Stored in RAM (1168) is a blade evacuation module (1126), a module of computer program instructions for useful in evacuating blades in a storage array that includes a plurality of blades according to embodiments of the present disclosure. The blade evacuation module (1126) may be configured for evacuating blades in a storage array that includes a plurality of blades by: detecting an occurrence of a blade evacuation event associated with one or more blades; iteratively until migration has completed for each of the blades associated with the blade evacuation event: selecting, in dependence upon a blade redundancy policy, one or more next blades to be evacuated from the storage array; migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, data stored on the next blade; and migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, storage array computational workloads executing on the one or more next blades; blocking write access to the blades associated with the blade evacuation event; copying, from the one or more next blades to one or more of the blades in the storage array that are not associated with the blade evacuation event, the data stored on the one or more next blades; initiating a garbage collection process on the one or more next blades, wherein the garbage collection process identifies valid data stored on the one or more next blades and invalid data stored on the one or more next blades; and writing the valid data identified by the garbage collection process to the one or more blades in the storage array that are not associated with the blade evacuation event; rebuilding the data stored on the one or more next blades utilizing redundancy data stored in the storage array; identifying authorities executing on the one or more next blades; initiating, on one or more of the blades in the storage array that are not associated with the blade evacuation event, execution of the authorities; and ceasing execution of the authorities on the one or more next blades; receiving a user-initiated request to evacuate the blades associated with the blade evacuation event; receiving a system-initiated request to evacuate the blades associated with the blade evacuation event; erasing the data stored on the blades associated with the blade evacuation event; presenting an indication that migration has completed for one or more of the blades associated with the blade evacuation event; detecting an occurrence of a blade evacuation event associated with one or more blades; iteratively until migration has completed for each of the blades associated with the blade evacuation event: selecting one or more next blades to be evacuated from the storage array; and migrating, from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event, all array-related content; migrating data stored on the one or more next blades to one or more of the blades in the storage array that are not associated with the blade evacuation event; migrating all storage array computational workloads executing on the one or more next blades to one or more of the blades in the storage array that are not associated with the blade evacuation event; migrating all array-related content from the one or more next blades to a system that is external to the storage array; placing all array-related content received from the system that is external to the storage array on the one or more blades in the storage array that are not associated with the blade evacuation event; migrating all array- related content from the one or more next blades to one or more blades in the storage array that are not associated with the blade evacuation event in dependence upon a migration policy; placing the blades associated with the blade evacuation event in a read-only mode; determining whether migration of one or more blades associated with the blade evacuation event can proceed; responsive to determining that migration of one or more blades associated with the blade evacuation event cannot proceed, detecting a system configuration change; and performing other steps as described above.

[00204] Also stored in RAM (1168) is an operating system (1154). Operating systems useful in computers configured for evacuating blades in a storage array that includes a plurality of blades according to embodiments described herein include UNIX™, Linux™, Microsoft XP™, AIX™, IBM's i5/OS™, and others as will occur to those of skill in the art. The operating system (1154) and blade evacuation module (1126) in the example of Figure 11 are shown in RAM (1168), but many components of such software typically are stored in nonvolatile memory also, such as, for example, on a disk drive (1170).

[00205] The example computer (1152) of Figure 14 also includes disk drive adapter (1172) coupled through expansion bus (1160) and bus adapter (1158) to processor (1156) and other components of the computer (1152). Disk drive adapter (1172) connects non-volatile data storage to the computer (1152) in the form of disk drive (1170). Disk drive adapters useful in computers configured for evacuating blades in a storage array that includes a plurality of blades according to embodiments described herein include Integrated Drive Electronics ("IDE") adapters, Small Computer System Interface ("SCSI") adapters, and others as will occur to those of skill in the art. Non-volatile computer memory also may be implemented for as an optical disk drive, electrically erasable programmable read-only memory (so-called "EEPROM" or "Flash" memory), RAM drives, and so on, as will occur to those of skill in the art.

[00206] The example computer (1 152) of Figure 14 includes one or more input/output ("I/O") adapters (1 178). I/O adapters implement user-oriented input/output through, for example, software drivers and computer hardware for controlling output to display devices such as computer display screens, as well as user input from user input devices (1 182) such as keyboards and mice. The example computer (1 152) of Figure 1 1 includes a video adapter (1 109), which is an example of an I/O adapter specially designed for graphic output to a display device (1 180) such as a display screen or computer monitor. Video adapter (1 109) is connected to processor (1 156) through a high speed video bus (1 164), bus adapter (1 158), and the front side bus (1162), which is also a high speed bus.

[00207] The example computer (1 152) of Figure 14 includes a communications adapter (1 167) for data communications with a storage system (1 184) as described above and for data communications with a data communications network (1100). Such data communications may be carried out serially through RS-232 connections, through external buses such as a Universal Serial Bus ('USB'), a Fibre Channel data communications link, an Infiniband data communications link, through data communications networks such as IP data

communications networks, and in other ways as will occur to those of skill in the art.

Communications adapters implement the hardware level of data communications through which one computer sends data communications to another computer, directly or through a data communications network. Examples of communications adapters useful in computers configured for evacuating blades in a storage array that includes a plurality of blades according to embodiments described herein include Ethernet (IEEE 802.3) adapters for wired data communications, Fibre Channel adapters, Infiniband adapters, and so on.

[00208] The computer (1 152) may implement certain instructions stored on RAM (1 168) for execution by processor (1 156) for evacuating blades in a storage array that includes a plurality of blades. In some embodiments, evacuating blades in a storage array that includes a plurality of blades may be implemented as part of a larger set of executable instructions. For example, the blade evacuation module (1126) may be part of an overall system management process.

[00209] Readers will appreciate that although the examples described above are described in terms where one set of blades are being evacuated, multiple sets of blades may be evacuated in parallel. In such an example, a first blade evacuation event may be received that is associated with a first set of blades and a second blade evacuation event may be received that is associated with a second set of blades. When two distinct sets of blades are being evacuated, array-related content on the blades that are associated with the first blade evacuation event should not be migrated to blades that are associated with the second blade evacuation event, and vice versa.

[00210] Readers will further appreciate that although the example methods described above are depicted in a way where a series of steps occurs in a particular order, no particular ordering of the steps is required unless explicitly stated. Example embodiments of the present invention are described largely in the context of a fully functional computer system for evacuating blades in a storage array that includes a plurality of blades. Readers of skill in the art will recognize, however, that the present invention also may be embodied in a computer program product disposed upon computer readable storage media for use with any suitable data processing system. Such computer readable storage media may be any storage medium for machine-readable information, including magnetic media, optical media, or other suitable media. Examples of such media include magnetic disks in hard drives or diskettes, compact disks for optical drives, magnetic tape, and others as will occur to those of skill in the art. Persons skilled in the art will immediately recognize that any computer system having suitable programming means will be capable of executing the steps of the method of the invention as embodied in a computer program product. Persons skilled in the art will recognize also that, although some of the example embodiments described in this specification are oriented to software installed and executing on computer hardware, nevertheless, alternative embodiments implemented as firmware or as hardware are well within the scope of the present invention.

[00211] The present invention may be embodied as an apparatus, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention. The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, RAM, a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, and so on. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

[00212] Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.

[00213] Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a LAN or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, FPGAs, or PLAs may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

[00214] Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

[00215] These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for

implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.

[00216] The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

[00217] The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of apparatuses, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware -based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

[00218] Readers will appreciate that the steps described herein may be carried out in a variety ways and that no particular ordering is required. It will be further understood from the foregoing description that modifications and changes may be made in various embodiments of the present invention without departing from its true spirit. The descriptions in this specification are for purposes of illustration only and are not to be construed in a limiting sense. The scope of the present invention is limited only by the language of the following claims.

Claims

CLAIMS What is claimed is:

1. A method for evacuating a blade in a storage system having a plurality of blades, performed by the storage system, comprising:

designating the blade for evacuation from the storage system; migrating data or metadata owned by one or more authorities of the blade from the blade to one or more further blades, of the plurality of blades, in the storage system, so as to result in the blade being evacuated and prepared for

decommissioning; and

decommissioning the blade from the storage system.

2. The method of claim 1 further comprising:

blocking write access to the blade designated for evacuation.

3. The method of claim 1 wherein the designating is performed with respect to a blade redundancy policy, the blade redundancy policy specifies a maximum number of blades that may be lost without resulting in a loss of data stored on the storage system and a number of additional blades selected to be evacuated from the storage system is less than or equal to the maximum number of blades that may be lost without resulting in loss of data stored on the storage system.

4. The method of claim 1 wherein migrating the data comprises copying, from the blade designated for evacuation to one or more other blades in the storage system that are not associated with the blade evacuation.

5. The method of claim 1 wherein migrating the data further comprises:

selecting, in dependence upon a blade redundancy policy, one or more next blades to be evacuated from the storage system;

initiating a garbage collection process on the one or more next blades, wherein the garbage collection process identifies valid data stored on the one or more next blades and invalid data stored on the one or more next blades; and

writing the valid data identified by the garbage collection process to the one or more blades in the storage system that are not evacuated.

6. The method of claim 5 wherein migrating the data stored on the one or more next blades further comprises rebuilding the data stored on the one or more next blades utilizing redundancy data stored in the storage system.

7. The method of claim 1 further comprising: selecting, in dependence upon a blade redundancy policy, one or more next blades to be evacuated from the storage system;

migrating storage system computational workloads executing on the one or more next blades selected to be evacuated ;

identifying authorities executing on the one or more next blades;

initiating, on one or more of the blades in the storage array that are not associated with blade evacuation, execution of the authorities; and

ceasing execution of the authorities on the one or more next blades.

8. The method of claim 1 wherein at least a portion of the data owned by one or more authorities the blades associated with the blade evacuation event is part of a data set that is striped across a plurality of blades.

9. An apparatus for evacuating blades in a storage system that includes a plurality of blades, the apparatus comprising a computer processor and a computer memory, the computer memory including computer program instructions that, when executed by the computer processor, cause the apparatus to carry out the steps of:

designating the blade for evacuation from the storage system;

migrating data or metadata owned by one or more authorities of the blade from the blade to one or more further blades, of the plurality of blades, in the storage system, so as to result in the blade being evacuated and prepared for decommissioning; and decommissioning the blade from the storage system.

10. The apparatus of claim 9 wherein:

the storage system includes a plurality of chassis, each chassis configured to support a plurality of blades; and

at least a portion of the system-related content is migrated from a blade mounted in the first chassis to a blade mounted in the second chassis.

1 1. The apparatus of claim 9 further comprising blocking write access to the blade

designated for evacuation.

12. The apparatus of claim 9 wherein the designating is performed with respect to a blade redundancy policy, the blade redundancy policy specifies a maximum number of blades that may be lost without resulting in a loss of data stored on the storage system and a number of additional blades selected to be evacuated from the storage system is less than or equal to the maximum number of blades that may be lost without resulting in loss of data stored on the storage system.

13. The apparatus of claim 9 wherein migrating the data comprises: copying, from the blade designated for evacuation to one or more other blades in the storage system that are not associated with the blade evacuation.

14. The apparatus of claim 9 wherein migrating the data further comprises:

15. The apparatus of claim 14 wherein migrating the data stored on the one or more next blades further comprises rebuilding the data stored on the one or more next blades utilizing redundancy data stored in the storage system.