GB2379769A

GB2379769A - System and method for managing storage resources in a clustered computing environment

Info

Publication number: GB2379769A
Application number: GB0225669A
Authority: GB
Inventors: Ahmad H Tawil; Nam V Nguyen
Original assignee: Dell Products LP
Current assignee: Dell Products LP
Priority date: 2000-03-09
Filing date: 2001-03-07
Publication date: 2003-03-19
Anticipated expiration: 2021-03-07
Also published as: GB2379769A8; GB2379769B; GB0225669D0

Abstract

A system and method for managing storage resources in a clustered computing environment. The method includes issuing a SCSI persistent reserve out command to reserve storage for a first node in response to receive a SCSI reservation command. The reservation may be released by issuing a SCSI reserve out command with a service action of clear. The system includes a resource management engine able to convert a SCSI reset command into a storage resource release command.

Description

SYSTEM AND METHOD FOR MANAGING STORAGE RESOURCES IN A CLUSTERED COMPUTING ENVIRONMENT The present disclosure relates in general to the field of data storage systems and, more particularly, to a system and method for managing storage resources in a clustered computing environment.

Storage area networks (SANs) often include a collection of data storage resources communicatively coupled to a plurality of nodes such as workstations and servers. In the present disclosure, the term"node"and "server"are used interchangeably, with the understanding that a "server" is one type of"node".

Within a SAN, a server may access a data storage resource across a fabric using the Fibre Channel protocol. The Fibre Channel protocol may act as a common physical layer that allows for the transportation of multiple upper layer protocols, such as the small computer system intercornect (SCSI) protocol. In a SAN environment, the SCSI protocol may assign logical unit numbers (LUNs) to the collection of data storage resources. The LUNs may allow a server within a SAN to access specific data storage resources by referencing a SCSI LUN for a specific data storage resource.

Though a Fibre Channel storage system can offer a great deal of storage capacity, the system can also be very expensive to implement. As a result, users often seek to share the available storage provided by the system among multiple servers. Unfortunately, if a server coupled to a given SAN uses the MICROSOFT WINDOWS NT (Trade Mark) operating system, the server may attempt to take ownership of any LUN visible to the server. For example, if a particular server detects several LUNs when the server boots, it may assume each LUN is available for its use. Therefore, if multiple WINDOWS NT (Trade Mark) servers are attached to a storage pool or a collection of data

storage resources, each server may attempt to take control of each LUN in the storage pool. This situation can lead to conflicts when more than one server attempts to access the same LUN.

A user seeking to solve this problem may partition or zone the available storage through filtering or through the use of miniport drivers that have LUN masking capabilities. In effect, this. partitioninq may prevent a server running WINDOWS NT (Trade Mark) from seeing storage capacity that is not assigned to it. This approach may be effective for stand-alone servers, but the approach has several shortcomings in a clustered computing environment.

Clustering involves the configuring of a group of independent servers so that they appear on a network as a single machine. Often, clusters are managed as a single system, share a common namespace, and are designed specifically to tolerate component failures and to support the addition or subtraction of components in a transparent manner. Unfortunately, because a cluster may have two or more servers that appear to be a single machine, the partitioning techniques mentioned above may prove an ineffective solution for avoiding conflicts when the two or more servers attemot to access the same LUN.

MICROSOFT CLUSTER SERVER (MSCS) (Trade Mark) embodies one currently available technique for arbitrating conflicts and managing ownership of storage devices in a clustered computing environment. An MSCS system may operate within a cluster that has two servers, server A, which may be in charge, and server B. In operation, server A may pass a

periodic heartbeat signal to server B to let server B know that server A is Baliven. If server B. does not receive a timely heartbeat from server A, server B may seek to determine whether server A is operable and/or whether server B may take ownership of any LUNs reserved for server A. Unfortunately, these MSCS system may utilize SCSI target resets during this process, and the SCSI resets may create several problems. For example, a typical SCSI reset in the MSCS system may cause all servers within a given Fibre Channel system to abort their pending input/output"I/O"processes. These aborted I/O processes may eventually be completed but not until the bus settles. This abort/wait/retry approach can have a detrimental effect on overall system performance.

In addition to this potential effect on performance, the MSCS system and its use of SCSI resets may have a detrimental effect on overall system reliability. In operation, the MSCS system may only account for one SCSI reset at a time. The inability to account for subsequent SCSI resets may lead to unexpected behavior and decrease system reliability.

In accordance with the present disclosure, a system and method for managing storage resources in a clustered computing environment are disclosed that provide significant advantages over prior developed techniques.

The disclosed system and method may allow for storage resource management and conflict arbitration with a reduced reliance on SCSI resets.

In co-pending British Patent Application, GB-A-2367162, from which the present case is divided, we disclose and claim a method for managing storage resources in a clustered computing environment including holding a reservation on a storage resource for a first node of the clustered computing environment. The node may be, for example, a server, a workstation, or any other computing device included within the cluster.

A third party process log out for the first node may be performed and the reservation held for the first node may be released. In one embodiment, the third party process log out may occur in response to a log out command sent on behalf of the first node. The third party process log out command may be sent, for example, by a second node or a Fibre Channel switch. The third party process log out command may include identification information that identifies the first node as the sender of the log out command even though the first node was not the actual sender. The identification information may include, for example, a world wide name and a source identifier assigned to the first node.

Managing storage resources in a clustered computing environment according to the disclosure in the co-pending case may additionally involve the zoning of a

Fibre Channel storage system. A zone may group a first node with a second node and a plurality of storage resources such as hard drives and other data storage devices. In the zoned system, a second node may log itself out after a third party process log out command has been issued for a first node. After the two nodes are logged out, a loop initialization protocol (LIP) link reset may be initiated, a state change notification may be generated, and any functioning nodes may re-login.

According to a first aspect of the present disclosure, a method for managing storage resources in a clustered computing environment

indudes receiving a sma"computer system interface (SCS !) It IL % % reservation command that seeks to reserve a storage resource for a node within the cluster- In response to the reservation command, a SCSI persistent reserve out command with a service action of reserve may be issued to reserve the storage resource for the node. This persistent reserve may hold a clearable reservation on the storage resource In one embodiment, the reservation may be cleared by issuing a SCSI persistent reserve out. command with a service action of clear The persistent reserve commands may allow LUN reservations to be individually released as opposed to clearing several LUN reservation at once with a SCSI reset.

According to a second aspect of the present disclosure, a computer system operable to manage storage resources in a clustered computing environment may include a first node, a second node, and a resource management engine operable to convert a SCSI reset command into a storage resource releasing command.

The system may also include a computer readable medium storing the may also include a computer readable medium storing the resource management engine and a central processing unit communicatively coupled to the computer readable medium and operable to execute the resource management engine.

In one embodiment, the system may also include a plurality of computing platforms communicatively coupled to the first node. These computing platforms may be, for example, a collection of networked personal computers.

The system may also include a Fibre Channel switch communicatively coupled to the first node and to a plurality of storage resources. The Fibre Channel switch may, in some embodiments, include a central processing unit operable to execute a resource management engine.

A system and method incorporating teachings of the present disclosure may provide significant improvements over conventional cluster resource management solutions.

For example, the disclosed techniques may be operable to better manage and arbitrate storage resource conflicts.

As discussed above, a-SCSI reset in a clustered computing environment can result in the initiation of an abort/wait/retry approach to several I/O processes, which can have a detrimental effect on overall system performance. The teachings of the present disclosure may help reduce reliance on SCSI resets and the resulting performance degradation In addition, the teachings of the present disclosure may facilitate the avoidance of system reliability problems associated with SCSI resets in a clustered computing environment. A conventional cluster resource

management system, such as MSCS, may be unable to account for SCSI resets initiated during the bus disturbance of an earlier SCSI reset. This limitation may lead to unexpected behavior and decrease system reliability.

Because the teachings of the present disclosure may facilitate the avoidance of at least some SCSI resets, system reliability may be improved.

Other technical advantages should be apparent to one of ordinary skill in the art in view of the specification, claims, and drawings.

The present invention will be described, by way of example, with reference to the accompanying drawings, in which : FIGURE 1 depicts a component diagram of a storage area network including one embodiment of a resource management engine that incorporates teachings of the present disclosure ; FIGURE 2 shows a flow diagram for a method for managing storage resources in a clustered computing environment in accordance with teachings of GB-A-2367162 ; and FIGURE 3 shows a flow diagram for an embodiment of a method for managing storage resources in a clustered computing environment in accordance with teachings of the present disclosure.

FIGURE 1 depicts a general block diagram of a storage area network (SAN), indicated generally at 10.

SAN 10 includes two clustered computing systems, clusters 12 and 14. As depicted, cluster 12 includes node 16 and node 18, and cluster 14 includes node 20 and 22. Nodes 16,18, 20, and 22 may be, for example, servers, workstations, or other network computing devices. As depicted in FIGURE 1, cluster 12 may be supporting a number of client devices such as the client personal computers representatively depicted at 24.

SAN 10 may also include a storage pool 26, which may include, for example, a plurality of physical storage devices such as hard disk drives under the control of and coupled to one or more storage controllers. The physical storage devices of storage pool 26 may be assigned LUNs.

Some physical storage devices may be grouped into RAID volumes with each volume assigned a single SCSI LUN address. Other physical storage devices may be individually assigned one or more LUNs. However the LUNs are assigned, the LUNs of FIGURE 1 may map the available physical storage of storage pool 26 into a plurality of logical storage devices and allow these logical storage devices to be identified and addressed.

In operation, nodes 16, 18, 20, and'22 may communicate with and transfer data to and from storage pool 26 through fabric 28 using fibre channel protocol.

As depicted in FIGURE 1, nodes 16 and 18 may be grouped into zone 30 with LUN1 and LUN2. Similarly, nodes 20 and 22 may be grouped into zone 32 with LUN3, LUN~4, and

LUM5. Using switch zoning to create zone 30 may prevent nodes 16 and 18 from seeing nodes 20 and 22. Similarly, using switch zoning to create zone 32 may prevent nodes 20 and 22 from seeing nodes 16 and 18. In addition to zoning, the embodiment of FIGURE 1 may employ LUN masking. LUN masking may blind a specific node or cluster from seeing certain LUNs. For example, LUN

masking may prevent nodes 16 and 1. 8 from seeing LUN3, LUN~4, and LUN5.

In the embodiment of FIGURE 1, nodes 16, 1. 8, 20, and 22 may be assigned a unique world wide name (WWN), which may be an eight byte identifier. The Institute of Electronics Engineers (IEEE) assigns blocks of WWNs to manufacturers so manufacturers can build fiber channel

devices with unique WWNs. For illustrative purposes, in the embodiment of FIGURE 1, node 16 may have a WWN of "AAA", node 18 may have a WWN of"BBB", node 20 may have a WWN of"CCC", and node 22 may have a WWN of"DDD". As such, nodes 16,18, 20, and 22 may be uniquely identifiable by other devices coupled to fabric 28.

Nodes 16,18, 20, and 22 may have identification information in addition to their respective WWNs. For example, according to the fibre channel protocol, when a node such as node 16 is initialized and logs into fabric 28, the node is assigned a fibre channel ID. This ID may be subject to change each time some initialization event occurs, for example, when another node or device logs into fabric 28. As depicted in FIGURE 1, fabric 28 has assigned fibre channel IDs as follows: node 16 is S~ID~1,

node 18 is S~ID~2, node 20 is S~ID~3, and node 22 is S ID 4.

In the embodiment of FIGURE 1, the various WWNs and fibre channel IDs may be stored in a computer readable medium 34, which may be accessible to devices of SAN 10.

As shown in FIGURE 1, SAN 10 may include a computing device 38. for establishing fabric 28. Such a computing device may include a CPU communicatively coupled to computer readable medium 34. Switch 36 may also have at least one port 40 for interfacing with other devices to form an overall fibre channel network.

In one embodiment of a system incorporating teachings of the present disclosure, computing device 38 may be operable to execute a resource management engine, which may be stored in computer readable medium 34. The resource management engine may be operable to perform several functions. For example, the resource management engine may be operable to access a maintained list of the WWNs and the fibre channel IDs of SAN 10 devices. In addition, the resource management engine may be operable to recognize a SCSI reset command issued by a node and to convert the command into a storage resource releasing command. The storage resource releasing command may be, for example, a third party process log out or a SCSI persistent reserve out command with a clear action.

In a typical MSCS cluster, a SCSI reset command may be issued when a node like node 18 or 20 fails to acknowledge receipt of a timely heartbeat 42 or 44 from a respective cluster mate- Heartbeats 42 and 44 may allow

nodes 18 and 22 respectively to"see"if their cluster mates are still functioning.

If, for example, node 18 can no longer"see"node 16, node 18 may seek to have any LUN reservations held for node 16 released. To accomplish this release, node 18 may send a SCSI reset command to initiate a low-level bus reset of the SCSI buses associated with nodes 16 and 18. In some systems, for example a MSCS system, node 18 may wait some specified amount of time before trying to reserve the LUNs that had been reserved by node 16. The waiting allows node 16 to regain control of the LUNs reserved to it before the SCSI reset. As such, if node 16 is"alive"despite node 18's failure to receive heartbeat 42, node 16 may be able to re-establish its resource reservations and in so doing let node 18 know that it is"alive".

Unfortunately, as mentioned above, a SCSI reset in a clustered computing environment can have a detrimental effect on overall system performance and system reliability. The disclosed system and resource management engine may help limit a clustered computing environment's reliance on SCSI resets in several different ways. Example techniques for avoiding SCSI resets may be better understood through consideration of FIGUREs 2 and 3.

FIGURE 2 depicts a flow diagram of a method 100 for managing storage resources in a clustered computing environment as described and claimed in our co-pending application GB-A-2367162. The method of FIGURE 2 may be implemented by a resource management engine executing on a storage controller attached to SAN

fabric. In some embodiments, the resource management engine may be executing on a CPU associated with a switch like switch 36 of FIGURE 1. In other embodiments, the CPU may be associated with a SAN device other than the switch. For example, a resource management engine may be executing on one or more nodes of a SAN.

During the operation of a SAN, a port login (PLOGI) command may be received. As is known in the art, a PLOGI ( command is a fibre channel command wherein a node logs into a storage device attached to a SAN. A node may execute a PLOGI command after the fabric has assigned a fibre channel ID (S~ID) to the node. As is also conventionally known, the SID of a node may be assigned when a node executes a fabric login (FLOGI) command.

At step 102, the S~ID and the WWN of a cluster node may be extracted. The extraction may occur at different times. For example, the extraction may occur when a node issues a PLOGI command. Once extracted, the SID and the WWN may be updated and may be stored in a computer readable medium. In some embodiments, this computer readable medium may be part of a SAN and may be accessible to several devices of the SAN.

At step 104, a LUN reservation may be held for a given node. In effect, the given node may have the exclusive right to use the reserved LUN. As is mentioned above, cluster nodes often communicate with one another using a heartbeat signal. At step 106, a SAN device may detect a failure to receive a timely heartbeat signal.

Though the failure to receive a heartbeat signal may only indicate a failed communication link between the

heartbeat sender and the heartbeat receiver, the failure may result, as shown at step 108, in the determination that a cluster node is inoperable.

In the embodiment of FIGURE 2, the determination that a node is inoperable, may cause another node to issue a SCSI reset. As shown at step 110, a SCSI reset command may be sent to release LUN reservations held for the node believed to be inoperable (the"dead"node). At step 112, the SCSI reset command may be converted into a third party process log out. This conversion may, for example, be performed by an executing resource management engine.

At step 114 a log out command for the "dead" node may be sent on the"dead"node's behalf by a third party.

For example, a resource management engine may access a computer readable medium storing the"dead"node's SID and WWN. The resource management engine may use the S - ID and the WWN of the"dead"node to log out the"dead" node. This third party process log out may result in the releasing of LUN reservations held for the logged out node.

As shown at step 116 of FIGURE 2, other nodes of a cluster may also log out or be logged out and a loop initialization protocol (LIP) link reset may be initiated. The LIP link reset of step 118 may be followed by step 120's generation of a state change notification. In the embodiment of FIGURE 2, the state change notification may cause active cluster nodes, nodes that are not dead, to perform a port login and to seek LUN reservations. The port login of active cluster nodes

may be seen at step 122. If the"dead"node was not dead, it may be able to regain its LUN reservations. If the "dead" node was dead, other cluster nodes may now be able to capture the LUN reservations held by the "dead" node. In effect, the storage resources held by the dead node will be made available to"live"nodes-resulting in a better utilization of storage resources without a SCSI reset.

An embodiment of a method 200 for managing storage resources in a clustered computing environment in accordance with the present invention may be seen in FIGURE 3. The method of F ! GURE 3, like the method of FIGURE 2, may be implemented by a resource management engine. This engine may be located at any number of places. For example, the engine may be located at a switch, a node, or a storage control attached to a Fibre Channel fabric.

As shown at step 202, method 200 may involve the receiving of a SCSI LUN reservation command. A typical SCSI reservation command may be cleared with a SCSI reset. As mentioned above, SCSI resets may cause a number of problems within a clustered computing environment. As such, at step 204, the SCSI reserve command may be converted to a SCSI persistent reserve out

c o command with a service action of RESERVE. The conversion from SCSI reserve to SCSI persistent reserve may be performed, for example, by an executing resource management engine. The persistent reserve out command may hold a persistent LUN reservation as shown at step 206 for the holding node, the node issuing the SCSI reserve command.

At step 208, it may be determined that the holding node is inoperable. In response to this determination, a SCSI reset command may be issued. The SCSI reset command of step 210 may be converted at step 212 to a SCSI persistent reserve command with a service action of CLEAR. In operation, the SCSI persistent reserve command with a service action of CLEAR may release the LUN reservations held by the initial SCSI persistent reserve out command. The LUN releasing of step 214 may effectively release storage resources held 1iy nodes determined to be inoperable at step 208. This may result in a better utilization of storage resources within a clustered computing environment, and the better utilization may be accomplished without employing SCSI resets.

Various changes to the above embodiment is contemplated by the present disclosure. For example, embodiments of the present disclosure may be implemented in SANs having any number of topologies. There may be, for example, numerous storage controllers, there may be a resource management engine executing on each node of a cluster, or there may be a single resource management engine executing within each zone of a clustered computing environment.

Claims

CLAIMS 1. A method for managing storage resources in a clustered computing environment, the method comprising: receiving a small computer system interface (SCSI) reservation command seeking to reserve a storage resource for a node of the clustered computing environment; and, in response to the reservation command, issuing a small computer system interface persistent reserve out command with a service action of reserve to reserve the storage resource for the node.
2 The method of Claim 1, wherein a miniport driver receives the reservation command and issues the persistent reserve out command.
3. The method of Claim 1 or Claim 2, further comprising releasing a reservation held for the node by issuing a small computer system interface persistent reserve out command with a service action of clear.
4. A computer system, comprising : a first node of a clustered computing environment; a second node of the clustered computing environment; and, a resource management engine operable to convert a small component system interface (SCSI) reset command into a storage resource releasing command.
5. The system of Claim 4, wherein the resource releasing command comprises a third party process log out.

<Desc/Clms Page number 19>
6. The system of Claim 4, wherein the resource releasing command comprises a small component system interface persistent reserve out command with a clear action
7. The system of any one of Claims 4 to 6, further comprising: a computer readable medium storing the resource management engine; and, a central processing unit communicatively coupled to the computer readable medium and operable to execute the resource management engine.
8. The system of Claim 7, further comprising: a plurality of computing platforms communicatively coupled to the first node; a Fibre Channel switch communicatively coupled to the first node; and, a plurality of storage devices communicatively coupled to the Fibre Channel switch.
9. The system of Claim 8, wherein the Fibre Channel switch comprises the central processing unit.