WO2015031540A1

WO2015031540A1 - Asynchronous file system migration

Info

Publication number: WO2015031540A1
Application number: PCT/US2014/053011
Authority: WO
Inventors: Derek Beard; Darrell Suggs; Fountain RAY; Gregory Dahl; Damon Fleury; Ryan Cox; Ghassan Yammine; Gregory Becker; Bryan VENTEICHER; Kris Meier; Gregory ALTHAUS; Duen-Wen Hsiao; Jason PRESTON
Original assignee: Netapp, Inc.
Priority date: 2013-08-27
Filing date: 2014-08-27
Publication date: 2015-03-05

Abstract

Examples described herein include a computer system, positioned in-line with respect to a plurality of clients that actively use a source file system, to replicate a source file system on a target memory in presence of out-of-band events which alter the source file system.

Description

ASYNCHRONOUS FILE SYSTEM MIGRATION

TECHNICAL FIELD

[0001] Examples described herein relate to a system and method for detecting out-of-band changes when replicating a source file system using an in-line system.

BACKGROUND

[0002] Network-based file systems include distributed file systems which use network protocols to regulate access to data . Network File System (NFS) protocol is one example of a protocol for regulating access to data stored with a network- based file system. The specification for the NFS protocol has had numerous iterations, with recent versions NFS version 3 (1995) (See e.g., RFC 1813) and version 4 (2000) (See e.g., RFC 3010). In general terms, the NFS protocol allows a user on a client terminal to access files over a network in a manner similar to how local files are accessed. The NFS protocol uses the Open Network Computing Remote Procedure Call (ONC RPC) to implement various file access operations over a network.

[0003] Other examples of remote file access protocols for use with network- based file systems include the Server Message Block (SMB), Apple Filing Protocol (AFP), and NetWare Core Protocol (NCP). Generally, such protocols support synchronous message-based communications amongst programmatic

components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1A illustrates a system for detecting out-of-band changes when replicating a source file system, according to an embodiment.

[0005] FIG. IB illustrates a data migration system that is operable to migrate data from a network file system, according to one or more embodiments.

[0006] FIG. 2A through FIG. 2E illustrate sequence diagrams that illustrate the stages of the data migration system 100. [0007] FIG. 3 illustrates a method for implementing a data migration system in stages to migrate a source file system without interruption of use to clients that use the source file system, according to an embodiment.

[0008] FIG. 4 illustrates a method for actively discovering and asynchronously replicating file system objects of a source file system while the source file system is in use, according to an embodiment.

[0009] FIG. 5 illustrates a method for passively discovering and

asynchronously replicating file system objects of a source file system while the source file system is in use, according to an embodiment.

[0010] FIG. 6 illustrates a method for conducting a pause and restart in the data migration, according to an embodiment.

[0011] FIG. 7A illustrates a method for detecting and handling OOB events during an active data migration in which a source filer is replicated at a

destination filer, according to one or more embodiments.

[0012] FIG. 7B illustrates a method for determining whether an out-of-band change resulted in a file handle being morphed, according to an embodiment.

[0013] FIG. 8 illustrates an example method for detecting and accommodating out-of-band changes in order to maintain cache coherency during data migration.

[0014] FIG. 9 illustrates a method for migrating data from a source file system to a destination file system while manipulating select attributes in order to maintain continuity of use by clients of the source file system, according to one or more embodiments.

[0015] FIG. 10 illustrates an example method for implementing data migration while preserving IP-based security policies of the source file system, according to an embodiment.

[0016] FIG. 11 is a block diagram that illustrates a computer system upon which embodiments described herein may be implemented . DETAILED DESCRIPTION

[0017] Examples described herein include a computer system, positioned inline with respect to a plurality of clients that actively use a source file system, to replicate a source file system on a target memory in presence of out-of-band events which may alter the source file system.

[0018] In an embodiment, a computer system performs operations that include populating a target memory with data corresponding to file system objects of the source file system. The computer system also handles requests from individual clients in the plurality of clients for file system objects of the source filer. In handling the requests, the computer system performs operations that include determining whether a file handle specified in a given request from a client identifies a file system object on the source file system that has a counterpart stored in the target memory. The determination can include determining whether the file handle specified in the given request identifies a first file system object on the source file system and a second file system object that is not the counterpart to the first file system object stored in the target memory. In response to determining that the file handle specified in the given request identifies the first file system object on the source file system and the second file system object in the target memory, the server removes the second file system object from the target memory and stores, in the target memory, the first file system object in association with the file handle specified in the given request.

[0019] A computer system includes one or more processors to replicate at least a portion of the source file system on a target memory, and to handle requests from individual clients for file system objects of the source file system. In handling requests, the one or more processors identify a file handle specified in a given request from one of the plurality of clients, and retrieve, from the source file system, a set of metadata associated with the specified file handle. From the set of metadata, the one or more processors determine whether an unrecorded change occurred on the source file system in connection with the specified file handle. The unrecorded change can correspond to at least one of (i) an update to a file system object for which a corresponding file system object exists in the target memory, where the update to the file system object is not reflected in the corresponding file system object. The unrecorded change can also correspond to a change in the file system object identified by the file handle at the source file system, as compared to the file system object identified by the file handle at the target memory. The computer system can update the target memory to record the change in connection with the specified file handle, so that the target memory is consistent with the source file system.

[0020] In still another embodiment, at least a portion of the source file system is replicated on a target memory while the source file system is in active use by a plurality of clients. Requests from individual clients for file system objects of the source file system can be received and handled by (i) identifying a file handle in the individual requests, (ii) retrieving, from the source file system, a set of metadata associated with the specified file handle, (iii) determining, from the set of metadata, that the file handle identifies a first file system object on the source filer and a second file system object on the target memory, and (iv) updating the target memory so that the file handle identifies the first file system object.

[0021] Still further, some embodiments described herein include a system for migrating data from a source file system to a destination file system, in a manner that is transparent and seamless to clients of the source file system.

[0022] In an embodiment, a data migration system includes a server

positioned in-line as between a plurality of clients and the source file system. The server transparently inserts in-line to receive and forward communications as between the source file system and individual clients of the source file system. While clients in the plurality of clients request use of the source file system, the server implements processes to replicate each file system object that is part of the source file system with the destination file system. In response to a client request that alters the source file system, the server can operate to (i) forward a response from the source file system to the requesting client, and (ii) queue a file system operation specified by the corresponding request, for performance at the destination file system after the response from the source file system has been forwarded to the one of the plurality of clients.

[0023] In another embodiment, file system objects that comprise a source file system can be replicated on a destination file system while the source file system handles file system operations from a plurality of clients that are mounted to the source file system. When the source file system and the destination file system are deemed to not be equivalent, a server asynchronously implements, on the destination file system, those file system operations that affect the source file system. Once the source file system and the destination file system are

programmatically deemed equivalent, file system operations that affect the source file system are implemented synchronously on the destination file system. Each of the plurality of clients can then transition from utilizing the source file system to using the destination file system.

[0024] Still further, in some embodiments, a data migration system that operates to migrate data from a source file system to a destination file system. Among the operations performed, the data migration system identifies a collection of file system objects that are associated with a source file system in active use by a plurality of clients. Individual file system operations that are intended to be handled by the source file system are intercepted at a location that is in-line and external to the source file system. The data migration system replicates each file system object of the collection at a destination file system. When individual file system operations are determined to alter the source file system, the data migration system asynchronously implements the one or more of the individual file system operations on the destination file system.

[0025] Still further, in some embodiments, a data migration system can implement a series of file system operations in order to traverse a source file system and identify file system objects that comprise the source file system. A data structure is maintained in which each identified file system object is associated with an entry and a current set of attributes for that file system object. Each identified file system object is created and maintained on a destination file system. Individual file system operations that are generated from clients for the source file system are intercepted at a node that is in-line and external to the source file system. A corresponding file system object specified by each of the file system operations is identified. A determination is made from the data structure as to whether the corresponding file system object has previously been identified. If the corresponding file system object has not previously been identified, then (i) determining a set of attributes for the corresponding file system object, (ii) adding an entry for the corresponding file system object and its set of attributes on the data structure, and (iii) replicating the corresponding data object at the

destination file system.

[0026] Examples described herein achieve numerous technical effects. Among them, a data migration system is provided to seamlessly migrate a file system to a destination while the file system is in active use by one or more clients. Once migrated, process of re-mounting clients can be done in staggered form to prevent disruption of the overall file system. Still further, a data migration system such as described can detect out-of-band changes which can disrupt a migration.

[0027] As used herein, the terms "programmatic", "programmatically" or variations thereof mean through execution of code, programming or other logic. A programmatic action may be performed with software, firmware or hardware, and generally without user-intervention, albeit not necessarily automatically, as the action may be manually triggered .

[0028] One or more embodiments described herein may be implemented using programmatic elements, often referred to as modules or components, although other names may be used. Such programmatic elements may include a program, a subroutine, a portion of a program, or a software component or a hardware component capable of performing one or more stated tasks or functions. As used herein, a module or component can exist in a hardware component independently of other modules/components or a module/component can be a shared element or process of other modules/components, programs or machines. A module or component may reside on one machine, such as on a client or on a server, or may alternatively be distributed among multiple machines, such as on multiple clients or server machines. Any system described may be implemented in whole or in part on a server, or as part of a network service. Alternatively, a system such as described herein may be implemented on a local computer or terminal, in whole or in part. In either case, implementation of a system may use memory, processors and network resources (including data ports and signal lines (optical, electrical etc.)), unless stated otherwise.

[0029] Furthermore, one or more embodiments described herein may be implemented through the use of instructions that are executable by one or more processors. These instructions may be carried on a non-transitory computer- readable medium. Machines shown in figures below provide examples of processing resources and non-transitory computer-readable mediums on which instructions for implementing one or more embodiments can be executed and/or carried. For example, a machine shown for one or more embodiments includes processor(s) and various forms of memory for holding data and instructions.

Examples of computer-readable mediums include permanent memory storage devices, such as hard drives on personal computers or servers. Other examples of computer storage mediums include portable storage units, such as CD or DVD units, flash memory (such as carried on many cell phones and tablets) and magnetic memory. Computers, terminals, and network-enabled devices (e.g . portable devices such as cell phones) are all examples of machines and devices that use processors, memory, and instructions stored on computer-readable mediums.

[0030] SYSTEM OVERVIEW

[0031] FIG. 1A illustrates a system for replicating a source file system, according to an embodiment. In some embodiments, a system 10 is implemented using one or more servers 20 that are positioned in-line with respect to clients 1 and a source file system ("source filer 12"). The source filer 12 can correspond to a network-based file system such as a distributed file system that is provided in a networked environment, under a protocol such as NFS Version 3 or Version 4. The source filer 12 can include logical components (e.g., controller) that structure distributed memory resources in accordance with a file system structure (e.g., directory-based hierarchy), as well process requests for file system objects 13 maintained as part of the source filer 12.

[0032] In an embodiment, the server 20 handles requests directed to the source filer 12 from clients 1, while implementing replication processes 16 to replicate at least a portion of the source filer 12 on a target memory 30. In some embodiments, the target memory 30 corresponds to a cache memory, and the server 20 implements the replication processes 16 in order to copy a portion of the source filer 12 into cache. For example, target memory 30 can be employed to cache at least the more frequently used file system objects of the source filer 12. In this way, the system 10 and target memory 30 can enhance the time of response to the clients 1 that make requests of the source filer 12. As an addition or variation, system 10 can be implemented as a data migration system which migrates data from the source filer 12 to a destination filer provided by the target memory 30. For example, as described with FIG. IB, and FIG. 2A through FIG. 2E, target memory 30 can correspond to a combination of cache and memory resources for providing a destination filer onto which the source filer 12 is replicated . As still another example, the target memory 30 can correspond to memory that backs up or archives the source filer 12.

[0033] As a result of the replication processes 16, the target memory 30 stores data corresponding to the file system objects 13 of the source filer 12. The data stored by the server 20 can include a data store 26 which associates each replicated file system object 17 (as stored in target memory 30) with a

corresponding metadata set 15, as well as with a corresponding file handle 19 that is in use for that file system object at the time the particular file system object is replicated . Thus, the stored metadata sets 15 can match or correlate to a corresponding metadata set for the file system object as provided though the source filer 12. Furthermore, in order to maintain an accurate replication, the server 20 intercepts requests 11 from clients 1 for the source filer 12. As described with, for example, FIG. IB, those client requests 11 which modify the source filer 12 can be replicated on the target memory 30 so that the target memory accurately reflects the source filer 12. When file system objects 13 of the source filer 12 are modified, the metadata set 15 of the corresponding file system object stored in the target memory 30 is updated to correlate to the updated state of that file system object in the source filer 12.

[0034] While server 20 intercepts the client requests 11, embodiments recognize that out-of-band ("OOB") changes can occur to the source filer 12. Such OOB reflect changes made to the source filer 12 from events other than those client requests 11 which are intercepted and handled by the server 20. For example, in an NFS environment, the server 20 may be unable to process requests made in alternative protocols, such as File Transfer Protocol ("FTP") . Still further, other changes to the source filer 12 can result from physical or local manipulation to the resources of the source filer 12.

[0035] The server 20 can operate to detect OOB changes made to at least the portions of the source filer 12 which are replicated on the target memory 30. In an embodiment, each client request 11 handled by the server 20 specifies a file handle 23 which identifies, on the source filer 12, a corresponding file system object 13. Upon receiving the request, the server 20 signals a retrieval 18 from the source filer 12 to obtain a set of metadata 21 for the file system object 13 identified by the file handle 19 of the client request 11. In the NFS environment, for example, the retrieval 18 can correspond to a "GetAttr" request from the source filer 12. Thus, for example, the server 20 executes the GetAttr request upon each incoming client request 11, or alternatively upon incoming client requests for which certain conditions are met (e.g., requests that specify replicated data from the target memory 30) .

[0036] The server 20 can include comparison logic 22 which performs operations that include : (i) using the file handle of an incoming client request 11 to identify a stored metadata set that is associated with the file handle and a corresponding file system object; (ii) retrieving a metadata set from the source filer 102 using the file handle of the incoming client request 11 ; and (iii)

comparing the retrieved metadata set 21 to the stored metadata set. For example, a comparison can be performed using the data store 26 in order to match the file handle 23 of the client request 11 against those file handles 19 that have been stored as a result of prior file system object replication and/or mirroring. When a match is found for the file handle 23 of the client request 11 in the data store 26, a comparison can be performed between the stored metadata set 15 and the retrieved metadata set 21. In one implementation, the metadata comparison can determine whether the file system object 13 identified by the file handle 23 in the client request 11 was updated or changed on the source filer 12, without a corresponding change being made at the target memory 30. For example, the compared metadata can include change time (or C-Time), which is time stamp that, in the NFS environment, is updated each time any change is made to an attribute or content of a corresponding file system object. If the C- Time of the retrieved metadata set 21 indicates a more recent change than that reflected in the corresponding stored metadata set 15, then the server 20 can determine that a change occurred with respect to at least the file system object identified by the file handle 23 of the client request 11. [0037] The compared metadata can also include modification time (or M- Time), which is time stamp that, in the NFS environment, is updated each time any change is made to a data content of a corresponding file system object. A change in the M-Time can signify, for example, an OOB write operation which modified the contents of the corresponding file system object.

[0038] The server 20 can associate a state with each replicated file system object 17 of the target memory 30. In one example, each replicated file system object can be associated with a state that corresponds to one of (i) valid, or (ii) suspect. If the state of the replicated file system object is deemed valid, the server 20 assumes the replicated file system object 17 is accurate as compared to a counterpart file system object provided by the source filer 12. The server 20 can, for example, determine that the file system object 17 is valid based on a comparison of the stored metadata set 15 associated with the file handle 19 of that file system object, and the retrieved metadata set 21 as returned from the source filer 12 when the request specifies the same file handle. In some

implementations, for example, when a particular file system object is deemed valid, the target memory 30 can be used to provide a response to a corresponding client request 11. Use of the target memory 30 in this way can, for example, enhance performance when compared to the source filer 12.

[0039] If the file system object 17 is deemed to be suspect, the server 20 implements processes to obtain a valid state in the data that is stored in the target memory 30. In some implementations, this may correspond to the server 20 removing the suspect file system object 17 from the target memory 30, and replicating a new file system object in its place. In alternative implementations, the server 20 may check the source filer 12 to see if a discrepancy exists in the respective metadata sets, and if no discrepancy in fact exists, the state can be switched to valid. Still further, in some instances, the state of the file system object can be switched to valid by updating the file system object 17 to reflect a change in attribute or data as recorded on the source filer 12. For example, an OOB change to the file system object on the source filer 12 can be replicated when discovered by the server 20 on the target memory 30.

[0040] In some embodiments, the replicated file system object 17 of the target memory 30 can obtain a suspect state in response to some condition or event, such as the passage of time. For example, the server 20 can implement a lease time for each replicated file system object. If, for example, a replicated file system object has not been updated or checked for a given duration of time when a corresponding client request 11 for that object is received, then the particular file system object can be deemed suspect. If, however, the comparison of the metadata yields a result that indicates the replicated file system object is accurate, the state of that file system object can be switched to valid.

[0041] Embodiments further recognize that in some cases, when the replicated file system object 17 becomes suspect, the file handle 19 that is stored in the data store 26 can be re-assigned by the source filer 12. Such an occurrence is referenced herewith as the file handle being morphed by the source filer 12. The morphing of a file handle on the source filer 12 can be the result of an OOB event. For example, the source filer 12 (who is the authority for the file handle

assignments) determines what file system object is identified by a given file handle. To further the example, a given file system object can be deleted from the source filer 12. In such instances, the source filer 12 may recycle an identifier that was previously used for the deleted file system object. The reuse of identifiers in this manner can result from an OOB event, in that the events may occur outside of the client requests 11 that are handled by the server 20. The server 20 can implement operations to detect such changes to identifiers, and further to update the target memory 30 so that the target memory is in sync with the source filer 12.

[0042] According to some embodiments, each replicated file system object is assigned an identifier that is internal to the server 20, so that the file system object can be uniquely identified on the server 20. The internal identifier of each file system object 17 can be determined based in part on the metadata set 15 associated with that object or its file handle. For example, as described with examples below, an object identifier or OID can be determined in part from the node identifier of the file system object, as maintained on the source filer 12. The data store 26 can associate such internal identifier 29 with the file handle 19 and stored metadata set 15 for each replicated file system object 17. In order to determine whether the file handle 19 of an otherwise suspect file system object has morphed, the retrieved metadata set 21 for that object is used to generate a temporary identifier that is internal to system 10. If the temporary internal identifier is present in the data store 26 so as to be associated with an existing file handle 19, then the server 20 determines that the file handle 19 of the suspect file system object 17 has not morphed. If, on the other hand, the temporary internal identifier is not present in the data store 26, so that no existing file handle 19 is associated with the identifier, then the determination of the server 20 is that the file handle has morphed. In such case, the server 20 may eliminate the prior replicated file system object and replicate the new file system object in association with the morphed file handle.

[0043] DATA MIGRATION EXAMPLE

[0044] FIG. IB illustrates another embodiment of a data migration system that is operable to migrate data from a network file system, without interrupting the ability of client terminals ("clients") to use the network file system, according to one or more embodiments. As shown by an example of a data migration system 100 operates to migrate data from a source filer 102 to a destination filer 104. Each of the source and destination filers 102, 104 can correspond to a network- based file system, such as those that utilize a protocol such as NFS Version 3 or Version 4. Each of the source and destination filers 102, 104 can include logical components (e.g., controller) that structure distributed memory resources in accordance with a file system structure (e.g., directory-based hierarchy), as well process requests for file system objects maintained as part of that file system.

[0045] In an example of FIG. IB, data is migrated from the source filer 102 while the clients 101 are mounted to and actively using the source filer. More specifically, the data migration system 100 initiates and performs migration of data from the source filer 102 while clients 101 are mounted to the source filer. Among other benefits, the data migration system 100 can migrate the data from source filer 102 to the destination filer 104 in a manner that is transparent to the clients, without requiring the clients to first unmount and cease use of the source filer. By way of example, an administrator of a network environment may seek to migrate data from the source filer 102 to the destination filer 104 as a system upgrade for an enterprise network, without causing any significant interruption to the services and operation of the enterprise network. [0046] According to some embodiments, the data migration system 100 is implemented through use of one or more in-line appliances and/or software.

Accordingly, the data migration system 100 can be deployed on a computer network in position to intercept client requests 111 directed to source filer 102. The data migration system 100 can include processes that provide a data file server 110, as well as cache/memory resources (e.g. , high-speed media) that enable queuing of operations and objects and caching of file system objects. In an example of FIG. IB, a transparent data migration system is deployed between the source filer 102 and the clients 101 while the clients actively use the source filer, without any network or reconfiguration of the endpoints. Among other benefits, the data migration system 100 operates independently, is self-contained, and installs in the network path between the clients and file servers.

[0047] With further reference to FIG. IB, the data migration system 100 can be implemented by, for example computer hardware (e.g., network appliance, server etc.) that is positioned in-line with respect to a source filer that is to be migrated. In particular, the data migration system 100 can be positioned

physically in line to intercept traffic between the clients and the source filer 102. Moreover, the data migration system 100 can provide a transparent virtualization of the source filer 102, so that the client terminals continue to issue requests for use of the source filer 102 for purpose of intercepting and proxying client/source filer exchanges. In implementation, the data migration system 100 can be operated to replicate the source filer to the destination filer 104 without requiring clients that are utilizing the source filer 102 to have to remount or otherwise interrupt use of the source filer.

[0048] In an embodiment, the transparency in the in-line insertion of the data migration system 100 is accomplished by configuring the data migration system to intercept and use traffic that is directed to the Internet Protocol (IP) address of the source filer 102. For example, an administrator of the network environment in system 10 can configure the data migration system 100 to utilize the IP addresses of the source filer 102, and further to forward traffic directed to the source filer after the traffic has been intercepted and processed . Moreover, return traffic directed from the source filer 102 to the clients 101 can be configured, through manipulation of the filer response, to appear as though the traffic is being communicated directly from the source filer. In this way, the data migration system 100 performs various replication processes to migrate the source filer 102 without disrupting the individual client's use of the source filer 102. As a result, the data migration system 100 is able to migrate data from the source filer 102, without interruption or performance loss to the clients 101.

[0049] In more detail, some embodiments provide for the data migration system 100 to include a data file server 110, a file/object lookup component 120, a replication engine 124 and a cache engine 132. The data migration system 100 can implement processes that initially populate the destination filer 104

asynchronously, while the clients actively use the source filer 102. Moreover, file system operations communicated from the clients 101 can be implemented asynchronously at the destination filer 104. The asynchronous nature of the replication and file system updates facilitates the ability of the data migration system 100 to eliminate or reduce latency and performance loss in respect to the client's use of the source filers. At some point when the source and destination filers 102, 104 are deemed equivalent, operations that affect file system objects of the source filer 102 can be replayed on the destination filer 104 in synchronized fashion. This allows for a subsequent stage, in which the destination filer 104 can be used in place of the source filer 102, in a manner that is transparent to the clients who have not yet unmounted from the source filer 102.

[0050] In an example of FIG. IB, the file system server 110 fields file system requests 111 from clients 101 while the replication engine 124 implements replication processes that populate and update the destination filer 104. In one implementation, the file system server 110 receives and processes NFS (version 3) packets issued from clients 101. Other file system protocols can also be accommodated. The file system server 110 can include logical components that summarize the protocol-specific request (e.g. , NFS request) before processing the request in a protocol-agnostic manner. The file system server 110 can also include logic that implement transactional guarantees for each NFS request. This logic can determine which NFS (or other protocol) requests are to be serialized, and which requests can be performed in parallel (e.g. , read-type requests). The file system server 110 identifies file system objects for replication through either active or passive discovery. In active discovery, a system process (e.g., "walker 105") traverses the source filer 102 to determine the file system objects 103. In passive discovery, requests communicated from the clients 101 that utilize the source filer 102 are inspected in order to identify file system objects that need to be migrated or updated on the destination filer 104.

[0051] As the file system server 110 handles requests from clients 101, source cache engine 132 can cache file system objects and metadata of file system objects. The source cache engine 132 can implement a variety of algorithms to determine which file system objects to cache. For example, the source cache engine 132 can cache file system objects on discovery, and subsequently identify those file system objects that are more frequently requested. In some

implementations, the metadata for the file system objects can be cached in a separate cache. Examples of metadata that can be cached include file handle, file size, C-time (change time) and M-time (modification time) attributes associated with individual file system objects (e.g., directories, folders, files).

[0052] In an example shown by FIG. IB, the source cache engine 132 includes a replay logic 133. The replay logic 133 can be implemented as a component that replays operations for creating, modifying or deleting file system objects the destination filer 104. As described below, the replay logic 133 can be implemented in one or more instances in connection with operations performed to update or replicate on the source filer 102.

[0053] The replication engine 124 operates to implement file system

operations that replicate file system objects of the source filer 102 and their existing states (as provided by the metadata) on the destination filer 104. As described below, the replication engine 124 can replicate file system objects using file system requests made on the source and destination filers 102, 104. As such, the replication engine 124 can be implemented as part of or in addition to the source cache engine 132. Moreover, the operations implemented through the replication engine 124 can be performed asynchronously. Accordingly, the replication engine 124 can utilize or integrate replay logic 133.

[0054] The client requests 111 to the file system server 110 may request file system objects using a corresponding file system handle. In some embodiments, the identification of each file system object 113 in client requests 111 can be subjected to an additional identification process. More specifically, client requests 111 can identify file system objects 113 by file handles. However, the source filer 102 may export multiple volumes when the clients 101 are mounted, and some clients 101 may operate off of different export volumes. In such instances, a file system object can be identified by different file handles depending on the export volume, and different clients may have mounted to the source filer using different export volumes, so that multiple file handles can identify the same file system object. In order to resolve this ambiguity, data migration system 100 utilizes an additional layer of identification in order to identify file system objects. In some embodiments, file system objects are correlated to object identifiers (OID) that are based in part on attributes of the requested object. An OID store 122 record OID nodes 131 for file handles (as described below), and further maintain tables which map file handles to OID nodes 131.

[0055] In an example of FIG. IB, the file/object lookup 120 uses the OID store 122 to map the file handle 129 of a requested file system object to an object identifier (OID) node 131. Each OID node 131 can include an OID key 137 for a corresponding file system object, as well as state information 159 for that file system object. The state information 139 can correspond to metadata that is recorded in the OID store 122 for the particular object.

[0056] In one implementation, the OID key 137 for each file system object can be based on attributes for the file system object. For example, the OID key 137 can be determined from a concatenation of an identifier provided with the source filer 102, a volume identifier provided with the source filer, and other attributes of the object (e.g., a node number as determined from an attribute of the file system object) . Accordingly, the properties that comprise the OID key 137 can be based at least in part on the file system object's attributes. Thus, if the file system server 110 has not previously identified a particular file system object, it will implement operations to acquire the necessary attributes in order to determine the OID key 137 for that file system object.

[0057] Once an OID node 131 is created, the file/object lookup 120 adds the OID node to the OID store 122. The OID store 122 can correspond to a table or other data structure that links the file handles of objects for given exports (or volumes) of the source filer 102 to OID keys 137, so that each OID key identifies a corresponding file system object.

[0058] FILE SYSTEM OBJECT DISCOVERY

[0059] In one implementation, a system client ("walker 105") or process can be used to traverse the source filer 102 independently of other requests made by clients 101 in order to actively discover objects of the source filer 102. The walker 105 can issue file system operations that result in a traversal of the source filer 102, including operations that laterally and vertically traverse a hierarchy of file system objects maintained with the source filer 102.

[0060] In addition to fielding requests from the walker 105, file system server 110 can also process request 111 from the various clients that actively use the source filer 102. When a request is received that specifies a file system object 113, file system server 110 uses the file handle 129 of the requested file system object to check whether an object identifier (OID) exists for the specified file handle. The request for a given file system object 113 can originate from any of the clients 101 that utilize the source filer 102, including the walker 105. In one embodiment, the file system server 110 communicates the file handle 129 to the file/object lookup 120. The file/object lookup 120 references the file handle 129 to determine if a corresponding OID node 131 exists. If an OID node 131 exists for the file handle 129, then the assumption is made that the corresponding file system objects 113 in the source filer 102 has previously been processed for data migration to the destination filer 104.

[0061] If the file/object lookup 120 does not identify an OID node 131 for the file handle 129, then the attributes of the newly encountered object is acquired . One of the components of the data migration system 100, such as the file system server 110 or replication engine 124, can issue a request 121 from the source filer 102 to obtain the attributes 123 of the newly discovered object. The request may be issued in advance of the file system server 110 forwarding the request to the source filer 102 for a response.

[0062] REPLICATION ENGINE [0063] In an embodiment, the file system server 110 processes individual file system requests 111, and determines the file handle 129 for each file system object. The OID store 122 can be maintained to store OID nodes 131 (for discovered objects) as tuples with corresponding file handles 129. When the file/object lookup 120 determines that no OID node 131 exists in the OID store 122 for a given file handle 129, then the replication engine 124 is triggered to replicate the corresponding file system object to the destination filer 104. Each node in the OID store 122 can further be associated with state information that records the state of the corresponding file system object relative to the source filer 102. In replicating the file system object, the replication engine 124 uses attributes of the replicated file system object so that the organizational structure of the portion of the source filer 102 where the replicated file system object is found is also maintained when replicated on the destination filer 104. In this way, the source filer 102 can be replicated with its organization structure and file system objects on the destination filer.

[0064] Additionally, as mentioned, an OID node is determined and added to the OID store 122. The entry into the OID store 122 can specify the OID node 131 of the new file system object, as well as state information as determined from the attributes of the corresponding file system object. In this way, the OID node 131 for the discovered file system object can be stored in association with the file handle 129 for the same object.

[0065] In one implementation, the replication engine 124 acquires the attributes 123 of the newly discovered file system object by issuing a file system attribute request 121 to the source filer 102. For example, in the NFS version 3 environment, the replication engine 124 can issue a "GetAttr" request to the source filer 102. In variations, other components or functionality can obtain the attributes for an unknown file system object.

[0066] Still further, in some variations, the source cache engine 132 can procure and cache the attributes of the source filer 102. When the attributes are acquired for a given OID node 131 (e.g., replication engine 124 issues GetAttr request), the request can made to the source cache engine 132, rather than to the source filer 102. This offloads some of the load required from the source filer 102 during the migration process. [0067] The replication engine 124 can implement processes to replicate a file system object with the destination filer 104. As mentioned, the replication engine 124 can operate either asynchronously or synchronously. When operating asynchronously, replication engine 124 schedules operations (e.g., via replay logic 133) to create a newly discovered file system object with the destination filer 104. The asynchronous implementation can avoid latency and performance loss that might otherwise occur as a result of the data migration system 100 populating the destination filer 104 while processing client request for file system objects.

[0068] According to some embodiments, the replication engine 124 can replicate the corresponding file system object by performing a read operation on the source filer 102 for the newly discovered file system object, then triggering a create operation to the destination filer 104 (or the destination caching engine 118) in order to create the discovered file system object on the destination filer. Examples recognize, however, that the source filer 102 may inherently operate to process requests based on file handles, rather than alternative identifiers such as OIDs. Accordingly, in requesting the read operation from the source filer 102, the replication engine 124 specifies a file handle that locates the same file system object with the source filer. Furthermore, the file handle used by the issuing client may be export-specific, and each export may have a corresponding security policy. For the source filer 102 to correctly recognize the read operation from the replication engine 124, the replication engine 124 can be configured to utilize the file handle that is specific to the client that issued the original request. By using the file handle of requesting client, the security model in place for the client can be mirrored when the read/write operations are performed by the replication engine 124. In one implementation, the OID store 122 may include a reverse lookup that matches the OID key 137 of the newly identified file system object to the file handle to which the request for the file system object was made. In this way, components such as the replication engine 124 can issue requests from the source and destination filers 102, 104, using the appropriate file handles.

[0069] In one implementation, the replication engine 124 can communicate the file system object 135 that is to be created at the destination filer to the replay logic 133. In turn, the replay logic 133 schedules and then performs the operation by communicating the operation to the destination filer 104. Thus, from the newly discovered file system object 135, the replay logic 133 can replicate the file system object 155 at the destination filer 104. The replay logic 133 can, for example, issue a create operation 159 to replicate the file system object 135 at the destination filer 104. The replicated file system object 155 can be associated with the same file handle as the corresponding file system object 135 maintained at the source filer 102.

[0070] In response to the create operation, the destination filer 104 returns a response that includes information for determining the OID for the replicated file system object 155 at the destination. For example, the replication engine 124 can use the response 149 to create a destination OID node 151 for the replicated file system object 155. The destination OID node 151 can also be associated with the file handle of the corresponding object in the source filer 102, which can be determined by the replication engine 124 for the requesting client (and the requesting client-specific export of the source filer). As such, the destination OID node 151 of the replicated file system object 155 is different than that of the source OID node 131.

[0071] The destination OID store 152 can maintain the destination node OID 151 for each newly created file system object of the destination filer 104. The mapper 160 can operate to map the OID node 131 of source file system objects to the OID node 151 for the replicated object at the destination filer 104.

Additionally, when the data migration has matured and the destination filer 104 is used to respond to clients that are mounted to the source filer 102, (i) the OID store 122 can map the file handle specified in the client request to an OID node 131 of the source filer 102, and (ii) the mapper 160 can map the OID node 131 of the source filer 102 to the OID node 151 of the destination filer 104. Among other uses, the mapping enables subsequent events to the file system object of the source filer 102 to be carried over and mirrored on the replicated file system object of the destination filer 104. Furthermore, based on the mapping between the OID nodes 131, 151, the determination can be made as to whether the requested file system object has been replicated at the destination filer 104.

[0072] Additionally, when the migration has progressed to the point that the destination filer 104 provides the responses to the client requests 111, the mapper 160 can translate the attributes of a file system object retrieved from the destination filer 104, so that the object appears to have the attributes of the corresponding object in the source filer 102. By masquerading attributes, the mapper 160 ensures responses from the destination filer 104 appear to originate from the source filer 102. This allows the clients to seamlessly be transitioned to the destination filer 104 without interruption.

[0073] In one variation, replication engine 124 triggers creation of the previously un-migrated file system object 135 in a cache resource that is linked to the destination filer 104. With reference to an example of FIG. IB, replication engine 124 triggers replication of file system object 135 to a destination cache engine 118, which carries a copy of the file system object in the destination filer 104.

[0074] In an embodiment, the replication engine 124 implements certain non- read type operations in a sequence that is dictated from the time the requests are made. In particular, those operations which are intended to affect the structure of the source filer 102 are recorded and replayed in order so that the organization structure of the destination filer 104 matches that of the source filer 102. In one implementation, the source cache 132 (or other component of the data migration system) records the time when a requested file system operation is received . The replay log 133 implements the timing sequence for queued file system operations. In this way, the dependencies of file system objects in the source filer 102 can be replicated on the destination filer 104. For example, operations specified from the clients 101 to create a directory on the source filer 102, then a file within the directory can be replicated in sequence so that the same directory and file are created on the destination filer, with the dependency (file within newly created directory) maintained.

[0075] FILE SYSTEM UPDATES

[0076] In addition to replicating newly discovered file system objects, data migration system 100 updates file system objects that have been replicated on the destination filer 104 with file system operations that are specified from clients 101 and directed to the source filer 102. The file system server 110 may signal the destination filer 104 the file system operations that alter objects of the source filer 102. Examples of such file system operations include those which are of type write, create, or delete. Read type operations, on the other hand, do not affect the objects of the source filer 102. When the request 111 from the clients 101 specify alteration operations (e.g ., write, create, delete), the file system server 110 (i) determines the OID for the specified file system object(s), (ii) communicates the operation 117 with the OID to the source cache engine 132 (which as described below uses replay logic 133 to schedule performance of the operation at the destination filer 104), and (iii) forwards the operation to the source filer 102 (with the file system handle) . The source filer 102 returns a response 127 to the file system server 110. The response 127 is communicated to the requesting client

101 in real-time, to maintain the transparent performance date of migration system 100. Accordingly, when the file system operation 119 is of a read type, it is forwarded to the source filer 102, and the corresponding response 127 is forwarded to clients 101.

[0077] The replay logic 133 operates to intelligently queue file system

operations that alter the source filer for reply at the destination filer 104. By way of example, replay logic 133 can implement hierarchical rule-based logic in sequencing when file system operations are performed relative to other file system operations. For example, file system operations that designate the creation of a directory may be performed in advance of file system operations which write to that directory. As another example, the replay logic 133 can determine when two operations on the same file system object cancel one another out. For example, an operation to create a file system object can be canceled by an operation to delete the same object. If both operations are queued, the replay logic 133 may detect and eliminate the operations, rather than perform the operations. Still further, during the asynchronous destination population stage, the replay logic 133 can detect when a given operation affects a portion of the source filer 102 that has yet to be replicated. In such instances, the replay logic 133 can ignore the operation, pending replication of the portion of the source filer

102 that is affected by the file system operation.

[0078] The replay logic 133 can include logic that replays the queued file system operations 117 in an appropriate sequence, through the destination cache engine 118. For example, the destination cache engine 118 can maintain file system objects of the destination filer 104. The replay logic 133 may implement the operations 117 on the destination cache engine 118 in order to preserve performance from the destination filer 104 as it replicates the source filer 102. As a variation, the replay logic 133 can directly replay the file system operations at the destination filer 104. When the data management system operates in synchronous or bypass (see FIG. 2C) mode, the destination cache engine 118 further preserve system performance and transparency.

[0079] Additionally, the responses 127 to client requests 111 from the source filer 102 can be inspected by the file system server 110 for metadata 141, including timing attributes for file system objects. The metadata can be stored in the OID store 122 as part of each file object's OID node. Additionally, when requests are issued on the destination filer 104, the responses from the

destination filer can be inspected by the replication engine 124, and attributes detected from the response can be stored with the corresponding destination OID node 151 in the destination OID store 152.

[0080] The mapper 160 can be used to link the OID nodes of the respective source and destination OID stores 122, 152, for purposes that include identifying destination objects specified in client requests to the source filer 102. Additionally, the mapper 160 can implement logic to compare attributes of corresponding OID nodes in order to determine whether, for example, the replicated object is up to date as compared the source object.

[0081] OOB DETECTION

[0082] Examples described herein recognize that the data migration system 100 should develop the destination filer 104 to be an accurate replication of the source filer 102, even in the presence of OOB events which circumvent the data migration system 100. For example, some implementations provide that while the data migration system 100 can operate to handle client requests 111 that are provided using NFS version 3 or 4, some client requests 109 can be issued through an alternative network protocol (e.g ., FTP), and as such bypass the data migration system 100. Such client requests may be considered OOBin that the data migration system 100 does not directly learn of the client requests 111. In other implementations, OOB events can result from logical or physical

manipulation of the source filer 102 by, for example, external events (e.g., administrator). Examples described herein provide that the data migration system 100 includes logic that learns of the change such OOB communications have on the source filer 102, when such events occur outside of the client requests 111 that are handled by the data migration system 100.

[0083] In an example of FIG IB, file system server 110 includes OOB

determination component 115. The OOB determination component 115 can perform operations to detect when replicated file system objects 155, stored in the destination filer 104 and/or destination cache engine 118, no longer match corresponding file system objects of the source filer 102. In one embodiment, the OOB determination component 115 processes individual client requests 111 to determine whether a specified file handle of the request corresponds to a file system object for which a corresponding replicated file system object exists.

Furthermore, as described with an example of FIG. 7A and FIG. 7B, OOB

determination component 115 uses metadata and attributes associated with the file system object as provided by source filer 102 at the time of the request, as well as with the file system object's replicated counterpart, in order to detect OOB events that have changed the source filer 102 with respect to the particular file system object. In more detail, FIG. 7A and FIG. 7B illustrates a method for detecting and handling OOB events that affect the destination filer 104 and/or destination cache engine.

[0084] STAGED MIGRATION

[0085] According to embodiments, data migration system 100 implements the migration of the source filer 102 in accordance with stages that affect the respective states of the source and destinations. FIG. 2A through FIG. 2E illustrate sequence diagrams that illustrate the stages of the data migration system 100.

[0086] FIG. 2A illustrates an insertion stage for the data migration system 203. In the insertion phase, the data migration system 203 is inserted in-line and transparently to intercept traffic as between a set of clients 201 and the source filer 202. The data management system can be configured to detect and process traffic bound for the IP address of the source filer 202. The IP addresses of the source filer 202 can be obtained programmatically or through input from an administrator in order to intercept incoming traffic without requiring clients to remount to the source filer 202.

[0087] By way of example, in an NFS environment, clients are programmed to reconnect to a mounted filer when a connection to the filer is terminated. The data migration system 203 can be inserted by terminating a client's existing connection with the source filer 202, then intercepting traffic to the source filer once the client attempts to re-set the network connection. The data migration system 203 then connects to the clients 201 and uses the IP address of the source filer in order to appear as the source filer. Once connected, the data migration system 203 acts as a proxy between the client and source filer. Clients 201 can issue requests 205 (e.g., NFS operations) for the source filer 202, which are intercepted and forwarded onto the source filer by the data migration system. The responses

206 can be received from the source filer 202 and then communicated to the requesting clients 201.

[0088] FIG. 2B illustrates a build stage during which the destination filer 104 is populated to include the file system objects of the source filer 102. In the build stage, clients 201 issue requests 211 (read type requests) and 213 (non-read type requests) specifying file system operations from the source filer 202. The source filer 202 uses the requests 211, 213 (which can include active discovery requests, such as issued from the walker 105) to determine the file system objects 215 that need to be created on the destination filer 204. In response to receiving requests 211, the data migration system 203 performs an OID check

207 to determine if the specified file system object 215 has previously been encountered (and thus migrated) .

[0089] As noted in FIG. IB, the OID check 207 can be implemented by the file/object lookup 120 which compares the file handle in the request with an OID store 122. If the specified file system object is known, then the file system object is not re-created at the destination filer 204. If the specified file system object is not known, then the data migration system 203 acquires the attributes 216 from the source filer 202 (e.g., "Getattr" request 217) and then creates 208 an OID node for the newly discovered object. With the OID node added, the object is replicated 214 at the destination filer 204. The replication of the object is performed asynchronously, using hardware such as cache resources which can queue and schedule the creation of the file system object with the destination filer 204.

[0090] While an example of FIG. 2B depicts the attribute request being made of the source filer 202, in some implementations, a caching resource (e.g ., source cache engine 132) can cache the attributes of some or all of the file system objects on the source filer 202. As such, the attribute request 217 can be implemented as an internal request in which the data migration system 203 uses its internal cache resources to determine the attributes of a newly discovered file system object.

[0091] In addition to replication, file system requests 213 (e.g ., write, create, or delete-type requests) which alter the source filer 202 are also scheduled for replay on corresponding file system objects in the destination filer 204. The data migration system 203 may implement, for example, replay logic 133 to

intelligently schedule and replay file system operations at the destination filer 204 that affect the contents of the source filer 202. Those operations which do not affect the contents of the source filer (e.g ., type read operations 211) are forwarded to the source filer 202 without replay on the destination filer 204.

[0092] FIG. 2C illustrates a mirroring stage during which the destination filer is synchronously updated to mirror the source file system 202. The mirroring stage may follow the destination build stage (FIG. 2B), after when the source filer 202 and the destination filer 204 are deemed substantially equivalent. In one implementation, the mirroring state may be initiated by, for example, an administrator, upon a programmatic and/or manual determination that the source and destination filers are substantially equivalent. In this stage, when the clients 201 issue requests that alter the source filer 202, the data migration system 203 generates a corresponding and equivalent request to the destination filer 204. The request to the destination filer 204 can be generated in response to the incoming request, without the source filer 202 having first provided a response. Read-type requests 221 can be received by the data migration system 203 and forwarded to the source filer 202 without any mirroring operation on the destination filer 204. The response 231 to the read operation 221 are forwarded to clients 201. Other types of client-requested operations, which can affect the contents of the source filer 202 (e.g., write, delete, create) are copied 225 and forwarded to the destination filer 204. When the requests 223 are received, a copy of the request 225 is generated and communicated synchronously to the destination filer 104. The copy request 225 is signaled independently and in advance of the source filer 202 providing a response 233 to the request 223. A response 235 from the destination filer 204 can also be received for the copy request 225. As a result, both the source filer 202 and destination filer 204 provide a corresponding response 233, 235.

[0093] The data migration system 203 can forward the response 233 from the source filer 202 to the requesting client 201. However, if the response 233, 235 from the source and destination filers are inconsistent, failure safeguards can be implemented. For example, the destination file system 204 may be directed to re- replicate the file system object of the source filer 202. As an alternative or variation, the data migration system 203 may revert to asynchronously updating the destination filer 204 until the inconsistency between the source and

destination filers is deemed resolved.

[0094] FIG. 2D illustrates a cut-over stage, when the destination filer 204 is used to handle client requests while the clients remain mounted to the source filer 202. As with the mirroring stage, the determination to enter the cut-over stage can be made programmatically and/or manually. In the cut-over stage, the clients 201 still operate to communicate with the source filer 202. However, the data migration system 203 operates to transparently forward the requests to the destination filer 204 for response, and also forwards the response from the destination filer to the clients 201. Thus, the data migration system 203 forwards the requests 241 to the destination filer 204, and not to the source filer 202.

Responses 243 to the read-type requests 241 are forwarded from the destination filer 204 to the clients 201.

[0095] In the cut-over stage, clients 201 operate under the perception that they are communicating with the source filer 202. In order to maintain the operability of the clients, the data migration system 203 operates to provide a programmatic appearance that the source filer 202 is in fact providing the response to the client requests. To maintain this appearance to the clients, the data migration system 203 can masquerade the responses 243, 247 to appear as though the responses originate from the source filer 202, rather than the destination filer 204.

[0096] In some embodiments, the data migration system 203 implements masquerade operations 238 on responses that are being forwarded from the destination filer 204 to the clients 201. In some implementations such as provided by NFS environments, the clients 201 require responses 243, 247 to include attributes that map to the source filer 202, rather than the destination filer 204. Certain metadata, such as time metadata, alters as a result of the replication and/or use of the corresponding object with the destination filer 204. While the metadata on the destination filer 204 is updated, in order for the clients 201 to process the responses 243, 247, the metadata needs to reflect the metadata as provided on the source filer 202 (which the client understands). The data migration system 203 performs masquerade operations 238 which translate the metadata of the responses 243, 247 to reflect the metadata that would be provided for relevant file system objects as carried by the source filer 202. By way of example, M-time of a file system object changes if the data of the

corresponding file system object changes. The fact that the file system object is returned from the destination filer 204 will mean that the file system object will have a different M-time than the source file system 202 if the file system object is not modified after it is migrated to the destination filer. In order to maintain the attributes of the responses 243, 247 consistent for clients 201, the data migration system 203 manipulates a set of attributes in providing the response to the client (e.g ., masquerades the attributes). Specifically, the attributes specified in the response to the clients are re-written to match the attributes as would otherwise be provided from the source filer. Thus, for example, the data migration system 203 manipulates, in the response provided back to the client, the attribute received from the destination filer corresponding to the m-time so that it matches the m-time as would otherwise be provided from the source filer 202. Other attributes that can be manipulated in this manner include, for example, file identifier and file system identifier. With reference to FIG. IB, the file system server 110 stores the attributes of file system objects as they are replicated and updated. For example, the file system server 110 can store current attributes by inspecting replies from the source filer 202, and storing the attributes of file system objects in their respective OID node 131. [0097] In addition to manipulating attributes in the response (e.g ., masquerading), data migration system 203 operates to confirm that when new objects are created on the destination filer 204, the file identifiers generated for the object are unique in the namespace of the source filer 202. In order to accomplish this, one embodiment provides that the data migration system 203 creates a file object (e.g ., dummy) in the source filer 202. The source filer 202 then creates file identifier for the new object, and the data migration system 203 is able to use the identifier as created by the source filer to ensure the newly created object of the destination filer 204 is unique in the namespace of the source filer 202.

[0098] FIG. 2E illustrates re-mount state, when the clients re-mount to the destination filer. According to some embodiments, clients 201 can be re-mount at the destination filer 204 at the convenience of the administrator. Moreover, the administrator can remount the clients to the destination filer 204 in rolling fashion (e.g. , one at a time) in order to ensure that any mishaps are isolated. When a client remounts, the destination filer 204 is exported for the client, and the client can use the destination filer with file handles and metadata that is specific to the destination filer 204. Exchanges 251, 253 between the clients 201 and the destination are conducted with the destination filer being the new source.

[0099] METHODOLOGY

[0100] FIG. 3 illustrates a method for implementing a data migration system in stages to migrate a source filer without interruption of use to clients that use the source filer, according to an embodiment. FIG. 4 illustrates a method for actively discovering and asynchronously replicating file system objects of a source file system while the source file system is in use, according to an embodiment. FIG. 5 illustrates a method for passively discovering and asynchronously replicating file system objects of a source file system while the source file system is in use, according to an embodiment. FIG. 6 illustrates a method for conducting a pause and restart in the data migration, according to an embodiment. FIG. 7A illustrates a method for detecting and handling OOB events during an active data migration in which a source filer is replicated at a destination filer, according to one or more embodiments. FIG. 7B illustrates a method for determining whether an OOB change resulted in a file handle being morphed, according to an embodiment. FIG. 8 illustrates an example method for detecting and accommodating out-of-band changes in order to maintain cache coherency during data migration. FIG. 9 illustrates a method for migrating data from a source file system to a destination file system while manipulating select attributes in order to maintain continuity of use by clients of the source file system, according to one or more embodiments. FIG. 10 illustrates an example method for implementing data migration while preserving IP-based security policies of the source file system, according to an embodiment. Examples such as described with FIG. 3 through FIG. 10 can be implemented using, for example, a system such as described with FIG. IB.

Accordingly, reference may be made to elements of FIG. IB for purpose of illustrating suitable elements or components for performing a step or sub-step being described .

[0101] With reference to FIG. 3, a data migration system is inserted in-line in the network path of clients that utilize the source filer (310). The insertion of the data migration system 100 can be transparent, so that the use of the source filer by the clients is not interrupted. In particular, the data migration system replicates data from the source filer into a destination filer without requiring the clients of the source file or to unmount from the source filer. In one

implementation, the data migration system 100 obtains the IP addresses of the source filer. The TCP network connection between the clients and the source filer 102 can be disconnected. When the clients attempt to reconnect to the source filer, the data migration system intercepts the communications to the source filer (e.g ., intercepts traffic with the IP address of the source filer 102), and then proxies communications between the clients and the source filer.

[0102] Once the data migration system 100 is operational to intercept and proxy traffic between the clients and source filer 102, the data migration system asynchronously populates the destination filer 104 (320) . This can include asynchronously replicating objects detected on the source filer 102 at the destination filer 104 (322). In one implementation, the file system objects of the source filer 102 are queued for replication at the destination filer 104.

[0103] In addition to replication, the source filer 102 can receive client requests that specify file system operations that modify the source filer 102 or its contents. In the asynchronous stage, file system operations that modify previously replicated objects of the source filer 102 are asynchronously replayed at the destination filer 104 (324), where they update the corresponding file system objects.

[0104] According to some embodiments, the data migration system can transition from asynchronously updating the destination filer 104 to synchronously updating the destination filer 104 (330) . Some embodiments provide for a threshold or trigger for transitioning from asynchronous replication and update to synchronous updating of the source filer 102. For example, the transition from asynchronous to synchronous mode can occur when the source and destination filer's 102, 104 are deemed to be equivalent, such as at a particular snapshot in time. When synchronously updating, any client request that modifies the source filer 102 is immediately replayed on the destination filer 104. Thus, for example, a replay request is issued to the destination filer 104 in response to a corresponding client request for the source filer 102. The replay request can be issued to the destination filer independent of the response from the source filer 102 to the client request. Thus, the file system objects of the source filer 102 and destination filer 104 are synchronously created or updated in response to the same client request.

[0105] At some point when the destination filer 104 is complete (or near complete), the data migration system 100 switches and provides responses from the destination filer 104, rather than the source filer 102 (340). The client can still issue requests to the source filer 102. Read-type operations which do not modify file system objects can be responded to from the destination filer 104, without forwarding the request to the source filer 102. Other non-read type operations that modify file system objects or the filer can be forwarded to the destination filer 104 for response to the client.

[0106] According to some embodiments, the data migration system 100 masquerades responses from the destination file 104 as originating from the source filer 102 (342). More specifically, the data migration system 100 alters metadata or other attributes (e.g ., timing attributes such as M-time) to reflect metadata of the corresponding file system object residing on the source filer 102, rather than the destination filer 104. This enables the client 101 to seamlessly process the response from the destination filer 104. [0107] At a subsequent time, the data migration of the source filer 102 may be deemed complete. The clients can be unmounted from the source filer 102, and remounted to the destination filer 104 (350). The unmounting and remounting of the clients can occur in a rolling fashion, such as one at a time. This allows an administrator to reconfigure the clients to use the destination filer 104 with minimal disruption.

[0108] With reference to FIG. 4, asynchronous replication of the source filer 102 can include active identification of file system objects, which are then replicated on the destination filer 104 (410). In one example, the source filer 102 is traversed to identify non-migrated file system objects (412) . A traversal algorithm can be deployed, for example, to scan the file system objects of the source filer 102. The traversal algorithm can be implemented by, for example, a client-type process (e.g., client process provided on server) that issues requests to the source filer 102 for purpose of scanning the source filer. The attributes for individual file system objects can used to determine whether the particular file system object had previously been migrated to the destination filer 104. If the data migration system 100 has not acquired the attributes for a file system object, then the object may be deemed as being non-migrated or newly discovered . Once identified, the attribute for each such file system object is retrieved (414).

[0109] From the attribute, the identifier for the file system object is

determined and recorded (420). The identifier can uniquely identify the file system object. A record of the file system object and its attributes can be made and stored in, for example, a corresponding lookup store. Additionally, the attributes of the file system object can be used to determine a state of the particular file system object.

[0110] The identified file system object can then be queued for replication at the destination file system 104 (430). For example, the replication engine 124 can schedule replication of the file system object at the destination filer 104.

[0111] With reference to FIG. 5, asynchronous replication of the source filer 102 can also include passive identification of file system objects, where file system objects are identified for replication from client communications that send requests (e.g ., NFS type requests) to the source filer 102. In implementation, the data migration system receives client request for file system objects that reside on the source filer 102 (510). A determination is made as to whether the file system object has previously been migrated to the destination filer (512) . As described with an example of FIG. IB, the determination may be based on the identifier of the file system object, which can be based in part on the attributes of the object. For example, an OID key can be determined for the file system object and then used to determine whether the object was previously migrated to the destination filer 104.

[0112] If the determination is that the object has previously been migrated, the client request is forwarded to the source filer 102 for a response (530). If, however, the determination is that the object has not previous been migrated, a sequence of operations may be queued and asynchronously implemented in which the file system object is replicated on the destination file system 104 (520). The asynchronous replication of the file system object enables the client requests to readily be forwarded to the source filer for response (530). If the forwarded request is a read-type request (532), a response is received from the source filer for the read request and forwarded to the client (540). If the forwarded request is a non-read type request that modifies are alters the source filer or its objects (534), then (i) the response is received from the source filer 102 and forwarded to the client (542), and (ii) the request from the client is queued for replay on a corresponding replicated file system object of the destination filer 104 (544) .

[0113] In FIG. 6, data migration system 100 can be initiated to migrate data from the source filer to the destination filer. As mentioned with various

embodiments, file system objects of the source filer 102 can be detected (e.g ., actively or passively), and attributes for the detected file system objects are recorded (610). Additionally, the attributes of file system objects can be recorded from responses provided by the source filer to client requests (620).

[0114] While the data migration system is taking place, the data migration system 100 and can be paused for a period of time, then restarted (622). For example, an administrator may pause the data migration system 100 prior to the completion of the asynchronous build stage. When paused, the source filer 102 remains in active use, and clients can modify the contents of the source filer by adding, deleting or modifying file system objects of the source filer. When the data migration system returns online, the data migration system does not know what changes took place while it was paused. Rather to initiate the whole process over, again, the data migration system 100 can reinitiate active and/or passive file system object detection.

[0115] When a file system object of the source filer's detected (630), the attributes of the file system object can be checked to determine whether that particular file system object represents a modification to the source filer that occurred during the pause (632). Specific attributes that can be checked include timing parameters, such as modification time (M-time). The OID node 131 (see FIG. IB) for a given file system object can also include its attributes as recorded at a given time. In the response to the client request (whether active or passive), the attributes of the file system object can be inspected and compared against the recorded values. A determination can be made as to whether the values of the file system object indicate that the file system object had been updated during the pause (635). If the determination indicates that the file system object was updated, then the particular file system object is replicated again on the

destination filer 104 (640). For example, the file system object can be queued by the replication engine 124 for replication at a scheduled time. If the determination indicates that the file system object was not updated, then no further re- replication is performed (642).

[0116] In an example of FIG. 7A, an incoming client request 111 is received at the file system server 110, where the request is processed to identify a specified file handle for a requested file system object of the source filer (710). The file system server 110 issues a request to the source filer 102 to retrieve a metadata set associated with the file handle (720) . Among other data items, the file system server 110 can include metadata such as the C-time and/or the M-time.

[0117] A determination is made as to whether the file handle specified in the client request 111 identifies a file system object that has previously been replicated (730). If the file handle is associated with a file system object that has not previously been replicated, then the file system server 110 initiates steps (732) to replicate the file system object on the destination filer. As part of the replication process, the metadata set for the file system object is recorded in association with the file handle, as well as the OID for the corresponding file system object (734). For example, the OID store 122 can associate each file handle with a metadata set for a corresponding file system object.

[0118] If, on the other hand, the file handle is associated with a file system object that has previously been replicated, then the OOB detection component 115 of the file system server 110 performs steps in order to see whether an OOB change affected the particular file system object (740). In performing the step, the OOB detection component 115 can compare metadata (which can be retrieved through performance of step 720) corresponding to time stamps, such as the C- time. In particular, one embodiment provides that a C-time is obtained in connection with a specified file handle as a result of the file system server 110 issuing, for example, a GetAttr request to the source filer 102. The retrieved metadata (e.g., C-time) is compared to recorded metadata for the file system object when the file system object was previously replicated (742).

[0119] A comparison can be made as to whether the compared metadata (e.g., C-time) is a match (750). If the compared metadata is a match, then the OOB determination component 115 can determine that file handle and the file system object of the request is valid, in that the file handle identifies a file system object on the source filer 102 which is accurately updated and reflected on the

destination filer 104 (754).

[0120] If, on the other hand, the compared metadata is not a match, the OOB determination component 115 can determine the nature of the OOB change (758). Specifically, the OOB determination component 115 can determine whether the file handle of the request either (i) identifies a file system object which was updated on the source filer 102, but not on the destination filer 104 (760), and/or (ii) has morphed so that the file handle identifies a file system object on the source filer 102 that is different than what was previously identified when the particular file system object was replicated (764).

[0121] If OOB change corresponds to a file system object which was updated on the source filer 102, but not on the destination filer 104, then one or more remedial steps can be performed in order to update the destination filer 104 to accurately reflect the source filer 102 (770) . The remedial steps can include, for example, re-replicating the file system object in question and/or updating the file system object in question in order to reflect the change from the OOB event.

[0122] If the OOB change corresponds to a file handle being morphed on the source filer 102 so as to point to a different file system object, then the identified file system object on the destination filer 104 can be removed, and replaced with the newly assigned file system object from the source filer (774). Thus, the file handle and the newly retrieved metadata can reference a different file system object in, for example, the OID store 122 and the destination filer 104. In order to determine whether the file handle has morphed on the source filer 102, the response from the source filer 102 can be analyzed in a manner described with FIG. 7B.

[0123] A method such as described with FIG. 7B can be implemented in, for example, determining the nature of the OOB change (see step 770 in FIG. 7A) . With reference to FIG. 7B, the metadata of the response is used to generate a temporary OID at the file system server 110 (776). The temporary OID can be referenced against a list of OIDs maintained in the store 122 to determine whether the temporary OID matches a known OID and corresponding file system object (778). A determination can be made as to whether the temporary OID matches an OID that is known (e.g. , previously generated and matched to file handle) (780) . If the OID is associated with the file handle, then the OOB determination component 115 can determine no OOB event occurred (782). If the OID is not associated with the file handle, then the OOB determination component 115 can determine that an OOB event did actually occur (784).

[0124] A data migration system such as described with an example of FIG. IB can utilize cache in order to enhance performance. In utilizing cache,

embodiments recognize that cache coherency can be affected in the presence of out-of-band changes to the source filer. Embodiments such as described provided by a data migration system as described in FIG. IB operate to maintain cache coherency in the face of out-of-band changes to the source filer 102. In particular, data migration system 100 supports deployment models in which the file system being cached is also accessed by clients and other sources through an out-of band (e.g ., non-NFS such as CIFS or iSCSI). When OOB changes are detected to the source filer 102, corresponding cache elements can be invalidated, updated or replaced . Additionally, in a data migration context, additional action(s) may be taken (e.g. pause the migration or warn the user).

[0125] Furthermore, some embodiments provide for the data migration system to maximize throughput by selectively implementing file system operations received from the clients in parallel . However, the implementation of file system operations in parallel can cause cache incoherency when OOB events occur that change the source filer 102.

[0126] With reference to FIG. 8, the data migration system 100 receives file system operations from clients 101 (802). The file system operations can be directed to the source filer 102, but intercepted by the data migration system 100 as part of a data migration session in which the source filer 102 is migrate to the destination filer.

[0127] The data migration system 100 processes read-type operations (810) in parallel (812). In the context of NFS, for example, read-type operations include READ, GETATTR, LOOKUP and ACCESS. By allowing parallel query operations for read-type operations, the data migration system 100 can obtain maximum throughput. As read-type operations do not change the attributes of the requested file system operations, no coherency issues arise with their parallel processing .

[0128] The data migration system 100 can also process update-type

operations (820). The update-type operations alter the attributes of the specified file system operations. As such, the performance of the operations is serialized (822). The update-type operations are serialized in that the data migration system receives the operations, then sequences the operations in the order received before forwarding the operations onto the source filer 102. The response from the source filer 102 is then paired to the forwarded requests based on timing.

[0129] The data migration system 100 can process write-type operations in parallel (830). To enable maximum throughput of write-type operations, the data migration system 100 allows for non-overlapping write-type operations to be sent to the backend storage controller of the source filer 102 in parallel (832).

However, embodiments recognize that a write-type request implicitly updates M- time and C-time attributes of a specified file system object. [0130] In order to maintain cache coherency, the data migration system 100 operates to process the write replies (returned from the source filer 102) in the order that the corresponding operations were processed on the source filer 102 (836). Typically, for write-type operations, each write-reply typically returns two sets of file system attributes for each file system object: (i) A pre-operation attribute set, corresponding to the file system object's attribute just before the write was executed on the source filer; and (ii) a post-operation attribute set, corresponding to the file system attributes just before the write operation was executed on the source filer 102. The data migration system 100 sorts the write replies chronologically based on the pre-operation attribute time in order to ensure that they are processed in order.

[0131] When the data migration system 100 receives a write reply from the source filer 102, it identifies if the C-Time in the pre-operation attribute of the reply matches the C-Time of the cached attribute (840) . If there is a match (842), then the reply is the next expected reply and it is processed immediately (844). If the pre-operation attribute does not match the expected value, then the reply is queued onto a sorted queue of pending replies, sorted chronologically by C-Time (846) . The subsequent write replies can be inspected to determine whether any of them are the next expected reply. When the next expected reply is received, the queue of pending replies is walked through to determine if the next expected value is queued. The reply queue processing stops again once the processing thread arrives at a reply whose pre-operation C-time attribute does not match that for the next expected value at that instance.

[0132] In order to support the detection of out of band events, data migration system 100 implements a timer for each queued write reply (850). More specifically, each write reply is associated with an expiration time, indicating the maximum amount of time a queued reply will wait for reply processing . This expiration time can serve, for example, the following purposes: (i) the expiration timer limits the amount of additional latency that will be added to a write reply; and (ii) the expiration timer enables detection of an OOB event for the file system object. The expiration of the timer thus indicates the occurrence of an OOB event (852). For example, if an OOB event does occur on a file system object, it will cause a write reply to come back with an unexpected pre-operation C-time. The data migration system 100 can insert this reply with an unexpected pre-operation attribute in the reply queue and it will remain pending until the timer expires, indicating that it should be processed . This timer expiration will force the processing of this reply as an OOB event and the data migration system 100 can invalidate the file system object.

[0133] An embodiment further recognizes that another implication of

processing writes in parallel with other operations is that the implicit attribute update of a write operation affects the attribute returned by query operations that were inflight at the same time as the write. For example, if a write request is sent to the source filer 102 in parallel with a read request, the controller of the source filer 102 may process the two operations in two different orders : (i) read before write, and (ii) write before read. In the read-before-write case, the attribute returned in the read reply will reflect the pre-write attribute. In the write-before- read case, the attribute returned in the read reply will reflect the post-write attribute. In either case, the data migration system 100 may be unable to use the attribute returned in the read reply to make a determination as to whether an OOB event occurred on the source filer 102. For example, unlike write replies, read-type operations do not separately return a pre-operation and post-operation set of attributes. Rather, such operations only return a single attribute.

[0134] According to some embodiments, the data migration system 100 can operate to guard against any tainted attribute returned by a query operation that was potentially affected by a parallel write (860). In one embodiment, a time period ("time zone") is initiated for a file system object when a write operation is requested from a client 101, but not completed (i.e., "inflight") (862). For a given file system object, a time zone begins when the data migration system 100 transitions from having no write operations in flight to having one or more write operations in flight. The time zone completes once all inflight write operations for the file system object have been processed .

[0135] In an embodiment, the data migration system 100 determines which query operations for a given file system object were inflight (initiated, but not yet processed) during the time zone for that file system object. For each operation, a counter is initiated when the time zone is present (872). Furthermore, the time zone is incremented for each operation that starts or completes on the object (874). Each request sent to the controller is stamped with a starting tick and each reply received is stamped with and end tick. Additionally, each object tracks the start and end tick of its current dynamic attribute zone.

[0136] Using this information, data migration system 100 determines when a completed operation was in transit during the time zone (880). The following may result from the determination : (i) If the file system object is currently in the time zone, the attribute in the reply is considered invalid (882) ; (ii) if the starting tick of the completed operation is after the ending tick of the last time zone, the attribute in the reply is considered valid (884); (iii) if the starting tick of the completed operation is before the ending tick of the last zone, the attribute is considered invalid (886). Any attributes from query replies declared as invalid are not used for OOB detection. Thus, the OOB detection is performed using attributes deemed valid.

[0137] With reference to FIG. 9, a data migration process is performed to migrate file system objects from the source filer 102 to the destination filer 104. For example, with reference to FIG. 2A through FIG. 2C, data migration system 100 can be inserted in-line with respect to clients and the source and destination filers 102, 104. An asynchronous replication process can be initiated while the clients 101 actively use the source filer 102. Furthermore, operations that affect the source filer 102 (e.g ., write operations) are mirrored on the destination filer. As shown by FIG. 2C, once the source filer 102 and the destination filer 104 are substantially equal, a mirroring state may occur in which file system operations specified in the client requests 111 for the source filer 102 are mirrored on the destination filer 104.

[0138] As shown by FIG. 2D, a cut-over stage can follow in which authority for responding to client requests 111 is transferred from the source filer 102 to the destination filer 104 (910).

[0139] Once authority is transferred, the data migration system 100 forwards client requests 111 to the destination filer 104 (920). This is in contrast to preceding stages in which the source filer 102 is used to provide the response to the client requests. [0140] Responses from the destination filer 104 are received and forwarded to the clients 101 (930). While responses are generated from the destination filer 104, examples recognize that the clients 101 operate in a manner that has them connected to the source filer 102, rather than the destination filer 104. Examples recognize that the clients 101 use of the source/destination filers can be disrupted if the attributes provided in the responses to the client requests include certain attributes which omit values carried on the source filer 102, but rather carry values from the destination filer 104. In such cases, the data migration system 100 operates to change the attributes in the responses of the destination filer 104, before forwarding those responses to the respective clients.

[0141] In more detail, examples described herein recognize that the file system objects specified in some responses to client requests 111 require one or more attributes to be manipulated (940). Among the attributes, the response from the destination filer 104 may need to include identifiers, such as the file handle or filer identifier, that originate from the source filer 102. Accordingly, attributes included in the response from the destination filer 104 can be mapped (e.g ., using mapper 160) to corresponding attributes provided by the source filer 102 (942) . For example, the destination OID 152, mapper 160 and OID store 122 can be used to map attributes provided in the response from the destination filer 104 to the attribute that would have otherwise been provided had the response originated from the source filer 102.

[0142] In some embodiments, time attributes of some file system objects specified in some responses the destination filer 104 can also be manipulated to reflect the time attribute of a corresponding file system object provided by the source filer 102 (944) . In one embodiment, a determination can be made for a given response as to whether a specified file system object should include an attribute of modification time (or M-time) as reflected for a corresponding file system object of the source filer (945). The M-time for a given file system object can be updated by a corresponding filer each time the file system object is modified . Accordingly, the determination can be based in part on whether the specified file system object was modified after the transfer in authority took place (e.g ., as shown in FIG. 2D) . If the file system object specified in the response from the destination filer 104 has not been modified since after the transfer, then the M-time of the source filer 102 is used in the response (946) . For example, the mapper 160 can use the M-time value provided in the OID store 122 to modify the attribute in the response provided from the destination filer 104, so that it includes the M-time as would have been provided from the source filer 102. Once the change has been made, the file system server 110 can forward the response back to the client 101. Alternatively, a programmatic component of the data migration system 100 (e.g., mapper 160) can retrieve a metadata set from the source filer 102 for the corresponding file system object.

[0143] Conversely, if the file system object specified in the response from the destination filer 104 has been modified since the transfer to the destination filer, then the M-time of the destination filer 104 is used in the response (948).

[0144] Other examples of attributes that can be modified by the file system server 110 include attributes which identify a user or user class. For example, the source filer 102 may have provided an export for the clients 101 that identify a set of users, and a different set of users may be defined on the destination filer 104. In such cases, the file system server 110 can again map an attribute of a user, as provided in the response from the destination filer 104, to one that is recognized or in use by the source filer 102.

[0145] Similarly, attributes that affect security policies can be mapped in instances when the security policies of the destination filer 104 do not match that of the source filer 102. For example, if the destination filer provides a response that includes attributes for a first security policy, the file system server 110 can determine whether the attribute would be in compliance with the security policy of the source filer 102. If there is no match, the source filer 102 can manipulate the attribute of concern so as to maintain the appearance of compliance with the security policy of the source filer 102.

[0146] Still further, some examples provide that the file system server 110 performs a fake object creation on the source filer 102 in cases such as when the client 101 requests the creation of a new file system object when authority has been transferred to the destination filer 104 (see FIG. 2D) . In such cases, the file system object and the metadata may be replicated on the source filer 102 in order to maintain consistency between the source and destination filer 102, 104. [0147] With reference to FIG. 10, data migration may be implemented and in progress, so that data is transferred from the source filer 102 to the destination filer 104 while the clients 101 continue to issue requests from the source filer (1010). A method such as described with FIG. 10 can be implemented during, for example, the cut-over stage, when data migration system 100 forwards client requests to the destination filer 104. At this stage, embodiments recognize that the destination filer 104 is unable to implement IP-based security policies that would otherwise be in force on the source filer 102 because the data migration system 100 is masking the true IP addresses of the client. Accordingly, data migration system 100 can discover and then implement the IP-based policies of the source filer 102 in connection with the cutover stage, in which the destination filer 104 receives and performs the file system operations requested from the source filer 102. The discovery and implementation of the IP-based policies can further be performed without interrupting the normal process by which clients 101 utilize the source filer 102, so that the data migration system's involvement in migrating the data while implementing the policies remains seamless and transparent to the clients.

[0148] In implementing the IP-based policies, the data migration system 100 identifies clients that request file system operations from the source filer 102 (1020). For example, the data migration system 100 can respond to requests from individual clients for file system objects and access.

[0149] From such requests, the data migration system 100 can identify the credentials of each client (1030) . For example, credentials provided in the client requests as provided by the Remote Procedure Call (RPC) protocol can be identified.

[0150] Once identified, the credentials can be used to issue a reference request to the source filer to access a reference file system object (1040). In one embodiment, the data migration system 100 creates reference file system objects (e.g ., test files) on the source filer 102. Each reference file system object can correspond to a resource that will not affect migration or requested contents of source filer 102 with respect to the client(s) that are issuing requests. As the source filer 102 may have multiple exports and a different set of security policies for each export, the data migration system 100 may create multiple sets of reference objects, with each set of objects being used to discover the security policies of a particular export.

[0151] Thus, according to some embodiments, the data migration system 100 can create multiple sets of test files for the different exports of the source filer 102. One implementation provides for creation of a test root file for each export of the source filer 102. Such a file can be created so as to designate a permission level corresponding to the root level - e.g., an administrator level user (1042). In one implementation, the reference request can specify the RPC credentials of a particular client, as determined from a corresponding client request. Another implementation provides for the creation of a read/write file for each export, where the read/write file that has no read access restrictions (1044) .

[0152] The source filer's response to the request generated from the data migration system 100 for the reference files can identify the permission level associated with a particular set of credentials (1050) for a particular export. For example, a given client credentials can be used to determine whether the client has root level permissions (from the root test file), or whether the client has general read-only access (from the read/write test file) . In variations, other test files can determine other permission levels for credential sets. The permission levels determined in this matter can be specific to a particular export of the source filer.

[0153] Once determined, the data migration system 100 can implement security policies based on the credentials of the individual clients, on behalf of the destination filer 104 (1060). For example, in a given export, the data migration system 100 denies those clients that have been identified as having read-only access with the ability to specify write-access operations. Likewise, the data migration system 100 may determine root-level access clients, and then deny non-root-level clients access to those file system objects which require root-level permission levels.

[0154] Additionally, if the client request identifies the client as a root user, but the determination is made that the user does not have root access on the particular export, the credentials in the request can be remapped to that of a pre- configured anonymous user. In such an implementation, the destination filer 104 can also be configured have a pre-determined response to the anonymous user. In one implementation, the access level of the pre-configured anonymous user can be set on the destination filer 104 by an administrator. For example, the pre- configured anonymous user can be set to have a lesser level of permission than the root level user.

[0155] COMPUTER SYSTEM

[0156] FIG. 11 is a block diagram that illustrates a computer system upon which embodiments described herein may be implemented. For example, in the context of FIG. IB and FIG. 2A through 2E, data migration system 100 (or 203) may be implemented using one or more computer systems such as described by FIG. 11. In the context of FIG. 1A, the server 20 can also be implemented using one or more computer systems such as described with FIG. 9. Still further, methods such as described with FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9 and FIG. 10 can be implemented using a computer such as described with an example of FIG. 9.

[0157] In an embodiment, computer system 1100 includes processor 1104, memory 1106 (including non-transitory memory), storage device, and

communication interface 1118. Computer system 1100 includes at least one processor 1104 for processing information. Computer system 1100 also includes a main memory 1106, such as a random access memory (RAM) or other dynamic storage device, for storing information and instructions to be executed by processor 1104. Main memory 1106 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 1104. Computer system 1100 may also include a read only memory (ROM) or other static storage device for storing static information and instructions for processor 1104. A storage device 1110, such as a magnetic disk or optical disk, is provided for storing information and instructions. The

communication interface 1118 may enable the computer system 1100 to

communicate with one or more networks through use of the network link 1120 (wireless or wireline) .

[0158] In one implementation, memory 1106 may store instructions for implementing functionality such as described with an example of FIG. 1A, FIG. IB, FIG. 2A through FIG. 2E, or implemented through an example method such as described with FIG. 3 through FIG. 10. Likewise, the processor 1104 may execute the instructions in providing functionality as described with FIG. 1A, FIG. IB, FIG. 2A through FIG. 2E, or performing operations as described with an example method of FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9 and FIG. 10.

[0159] Embodiments described herein are related to the use of computer system 1100 for implementing the techniques described herein. According to one embodiment, those techniques are performed by computer system 1100 in response to processor 1104 executing one or more sequences of one or more instructions contained in main memory 1106. Such instructions may be read into main memory 1106 from another machine-readable medium, such as storage device 1110. Execution of the sequences of instructions contained in main memory 1106 causes processor 1104 to perform the process steps described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement embodiments described herein. Thus, embodiments described are not limited to any specific combination of hardware circuitry and software.

[0160] Although illustrative embodiments have been described in detail herein with reference to the accompanying drawings, variations to specific embodiments and details are encompassed by this disclosure. It is intended that the scope of embodiments described herein be defined by claims and their equivalents.

Furthermore, it is contemplated that a particular feature described, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments. Thus, absence of describing combinations should not preclude the inventor(s) from claiming rights to such combinations.

Claims

NETP. P151W0 WO 2015/031540 PCT/US2014/053011 What is claimed is :

1. A method for migrating file system data, the method being implemented by one or more processors and comprising :

identifying a collection of file system objects that are associated with a source file system that is actively in use by a plurality of clients;

intercepting individual file system operations that are intended to be handled by the source file system at a location that is in-line and external to the source file system, so as to not disrupt the plurality of clients requesting file system operations to be performed on the source file system;

for at least a duration of time during which the source file system is in active use by the plurality of clients,

replicating at least a portion of the source file system, including each file system object of the collection, at a destination file system;

determining when individual file system operations alter the source file system; and

asynchronously implementing one or more of the individual file system operations that are determined to alter the source file system on the destination file system.

2. The method of claim 1, further comprising :

determining when the source file system and the destination file system are equivalent; and

synchronously implementing the individual file system operations that are determined to alter the source file system on the destination file system.

3. The method of claim 1, wherein intercepting the individual file system operations includes communicating with individual clients from the location of the source file system.

4. The method of claim 1, further comprising :

forwarding the individual file system operations to the source file system; receiving a response to each of the individual file system operations; and determining, from the response of one or more of the individual file system operations, a set of attributes of a corresponding file system object. NETP. P151W0

WO 2015/031540 PCT/US2014/053011

5. The method of claim 4, further comprising storing the set of attributes in association with the corresponding file system object, the set of attributes including one or more timing parameters.

6. The method of claim 1, wherein replicating at least the portion of the source file system is performed asynchronously.

7. The method of claim 1, wherein asynchronously implementing one or more of the individual file system operations includes (i) generating a replay log that sequences multiple file system operations corresponding to a create type operation, a write type operation or a modification type operation, but not a read type operation, and (ii) asynchronously implementing the multiple file system operations from the replay log.

8. The method of claim 7, wherein asynchronously implementing one or more of the individual file system operations is performed while some file system objects of the collection are or have yet to be replicated with the destination file system.

9. The method of claim 1, wherein asynchronously implementing one or more of the individual file system operations includes determining that a given file system object specified by a given one of the file system operations has been replicated, then asynchronously implementing the given one of the file system operations in response to determining that the given file system object has been replicated .

10. The method of claim 1, wherein :

asynchronously implementing one or more of the individual file system operations is performed during a time period in which the source file system and the destination file system are deemed to not be equivalent; and

wherein the method further comprises:

once the source file system and the destination file system are deemed equivalent, NETP. P151W0

WO 2015/031540 PCT/US2014/053011

(i) synchronously implementing file system operations that affect the source file system on the destination file system; and

(ii) transitioning each of the plurality of clients from utilizing the source file system to using the destination file system.

11. The method of claim 10, wherein transitioning each of the plurality of clients includes switching from using the source file system to using the destination file system to respond to file system operations from the plurality of clients.

12. The method of claim 10, wherein transitioning each of the plurality of clients includes unmounting each of the plurality of clients from the source file system and mounting the client to the destination file system.

13. The method of claim 1, further comprising :

copying a portion of the file system objects that comprise the source file system into a source cache resource; and

using the source cache resource to respond to requests from clients for individual file system objects of the portion.

14. The method of claim 1, further comprising :

15. The method of claim 1, wherein the method comprises, performing during a transition period :

(a) forwarding requests for the source file system, from individual clients in the plurality of clients, to the destination file system;

(b) receiving responses from the destination file system to the requests from the individual clients in the plurality of clients;

(c) for one or more of the responses, manipulating one or more attributes of a file system object provided at the destination file system as specified in the NETP. P151W0

WO 2015/031540 PCT/US2014/053011 response, so that the one or more attributes each match an attribute for a corresponding file system object in the source file system ; and

(d) forwarding each of the responses to a requesting one of the plurality of clients, including the one or more responses that include the manipulated one or more attributes.

16. The method of claim 15, wherein the one or more attributes correspond to one or more attributes selected from a group consisting of a time stamp, file identifier, file system identifier and user identifier.

17. The method of claim 15, wherein the method further comprises:

signaling the destination file system to perform a set of file system operations that are specified in the requests from the individual clients in the plurality of clients and which affect the source file system; and

receiving and forwarding responses from the source file system to the individual clients who requested use of the source file system.

18. The method of claim 15, wherein manipulating the one or more attributes includes manipulating a time stamp of when the file system object was modified when the time stamp is specified in the response.

19. The method of claim 18, wherein manipulating the time stamp includes providing the time stamp from the source file system in the response only when the file system object was last modified during the transition period.

20. The method of claim 15, wherein manipulating the one or more attributes includes manipulating a change time of when the file system object was created when specifying the change time in the response.

21. The method of claim 1, wherein the method further comprises :

identifying, from one of the individual file system operations, a given request that specifies a file handle;

retrieving, from the source file system, a set of metadata associated with the specified file handle; NETP. P151W0

WO 2015/031540 PCT/US2014/053011 determining, from the set of metadata, that the file handle identifies a first file system object on the source file system and a second file system object on the destination file system; and updating the destination file system so that the file handle identifies the first file system object.

22. The method of claim 21, wherein determining includes comparing a time stamp in the set of metadata with a corresponding time stamp associated with the file handle in the destination file system.

23. The method of claim 1, further comprising :

identifying individual clients in the plurality of clients who direct

communications to the source file system while the file system data is migrated; determining a set of credentials for each identified client;

issuing, on behalf of each identified client and from a location that is external to the source file system, a request to the source file system to access a reference file system object, the reference file system object being associated with a known permission level ;

determining a permission level of each client based on a response from the source file system; and

implementing a security policy of the source file system for each client when, during the data migration, data from the destination file system is used to provide a response to a file system operation originating from any of the plurality of client.