Instantaneous restoration of a production copy from a snapshot copy in a data storage system

• US 6,957,362 B2
• Filed: 08/06/2002
• Issued: 10/18/2005
• Est. Priority Date: 08/06/2002
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Armangau, Philippe
• Primary Examiner(s): Beausoliel, Robert
• Assistant Examiner(s): Chu, Gabriel L.
• Application Number:
  US10/213,335
• Publication Number:
  US 20040030951A1
• Time in Patent Office: 1,169 Days
• Field of Search: 714/15, 714/16, 714/19, 714/20
• US Class Current: 714/20
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 11/1469 Backup restoration techniques
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

A data storage system maintains a production dataset supported by a clone volume, and multiple snapshot datasets supported by respective save volumes in a snapshot queue. In order to instantaneously restore the production dataset with the state of any specified snapshot, the data storage system responds to requests for read/write access to the production dataset by reading from the specified snapshot dataset and writing to the production dataset. The data storage system keeps a record of data blocks that have been modified by writing to the production dataset. The data storage system initiates a process of copying data blocks from the specified snapshot dataset to the production dataset if the record of the data blocks indicates that the data blocks have not yet been modified by writing to the production dataset.

Claims

1. A data storage system for providing access to a production dataset and at least one snapshot dataset, the data storage system comprising storage containing the production dataset and the snapshot dataset, the snapshot dataset being the state of the production dataset at a point in time when the snapshot dataset was created,

the data storage system being programmed for instantaneous restoration of the production dataset with the state of the snapshot dataset by initiating read/write access through a foreground routine to what appears to be a restored version of the production dataset while the production dataset is being restored by a background routine, the foreground routine keeping a record of data blocks that have been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine, the background routine copying data blocks from the snapshot dataset to the production dataset if said record of the data blocks indicates that the data blocks have not yet been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine.

2. The data storage system as claimed in claim 1, wherein the foreground routine provides read access to the snapshot dataset and write access to the production dataset.

3. The data storage system as claimed in claim 1, wherein the data storage system is programmed for terminating read/write access through the foreground routine when the background routine has finished copying data blocks from the snapshot dataset to the production dataset.

4. The data storage system as claimed in claim 1, wherein the data storage system is programmed for performing a process of creating a snapshot copy of the restored production dataset concurrent with the restoration of the production dataset, the process of creating the snapshot copy using the record of data blocks in the production dataset that have been modified, in order to save original content of at least some of the data blocks being modified by the read/write access through the foreground routine.

5. The data storage system as claimed in claim 1, further comprising storage containing a clone volume of data blocks supporting the production dataset and at least one save volume supporting the snapshot dataset, the save volume containing original content of corresponding data blocks in the clone volume existing at a time of creation of the snapshot dataset, wherein the background routine copies the content of each data block in the save volume to the corresponding data block in the clone volume if the record of data blocks in the production dataset that have been modified indicates that the corresponding data block has not been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine.

6. A data storage system for providing access to a production dataset and at least one snapshot dataset, the data storage system comprising storage containing the production dataset and the snapshot dataset, the snapshot dataset being the state of the production dataset at a point in time when the snapshot dataset was created, the data storage system being programmed for instantaneous restoration of the production dataset with the state of the snapshot dataset by responding to requests for read/write access to the production dataset by reading from the snapshot dataset and writing to the production dataset, and keeping a record of data blocks that have been modified by said writing to the production dataset, and initiating a process of copying data blocks from the snapshot dataset to the production dataset if said record of the data blocks indicates that the data blocks have not yet been modified by said writing to the production dataset.

7. The data storage system as claimed in claim 6, wherein the data storage system is programmed for responding to completion of the process of copying data blocks by no longer responding to subsequent requests for read access to the production dataset by reading from snapshot dataset and instead responding to subsequent requests for read access to the production dataset by reading from the production dataset.

8. The data storage system as claimed in claim 6, wherein the data storage system is programmed for deleting the snapshot dataset when the process of copying data blocks has been completed.

9. The data storage system as claimed in claim 6, wherein the data storage system is programmed for performing a process of creating a snapshot copy of the restored production dataset concurrent with the restoration of the production dataset, the process of creating the snapshot copy using said record of data blocks that have been modified, in order to save original content of at least some of the data blocks being modified by said writing to the production dataset.

10. The data storage system as claimed in claim 6, further comprising storage containing a clone volume of data blocks supporting the production dataset and at least one save volume supporting the snapshot dataset, the save volume containing original content of corresponding data blocks in the clone volume existing at a time of creation of the snapshot dataset, wherein the background routine copies the content of each data block in the save volume to the corresponding data block in the clone volume if said record of data blocks that have been modified indicates that the corresponding data block has not been modified by said writing to the production dataset.

11. A file server for providing access to a production file system and a plurality of snapshot file systems, each of the snapshot file systems being the state of the production file system at a respective point in time when said each of the snapshot file systems was created,

said file server comprising storage containing a clone volume of data blocks supporting the production file system, and the storage containing, for each of the snapshot file systems, a respective save volume of data blocks supporting said each of the snapshot file systems,

the respective save volume of said each of the snapshot file systems containing data blocks having resided in the clone volume at the respective point in time when said each of the snapshot file systems was created,

the file server being programmed for maintaining the save volumes in a snapshot queue in a chronological order of the respective points in time when the snapshot file systems were created, the save volume supporting the oldest one of the snapshot file systems residing at the head of the snapshot queue, and the save volume supporting the youngest one of the snapshot file systems residing at the tail of the snapshot queue,

the file server being programmed for performing a read access upon the production file system by reading from the clone volume,

the file server being programmed for performing a write access upon the production file system by writing to the clone volume but before modifying a block of production file system data in the clone volume, copying the block of production file system data from the clone volume to the save volume at the tail of the snapshot queue if said block of production file system data in the clone volume has not yet been modified since the respective point in time of creation of the snapshot file system supported by the save volume at the tail of the snapshot queue,

the file server being programmed for performing a read access upon a specified data block of a first specified one of the snapshot file systems by reading from the save volume supporting the first specified one of the snapshot file systems if the specified data block is found in the save volume supporting the first specified one of the snapshot file systems, and if the specified data block is not found in the save volume supporting the first specified one of the snapshot file systems, searching for the specified data block in a next subsequent save volume in the snapshot queue, and if the specified data block is found in the next subsequent save volume in the snapshot queue, reading the specified data block from the next subsequent save volume in the snapshot queue, and if the specified data block is not found in any subsequent save volume in the snapshot queue, then reading the specified data block from the clone volume;

wherein the file server is programmed for instantaneous restoration of the production file system with the state of a second specified one of the snapshot file systems by creating a new snapshot file system and responding to subsequent requests for access to the production file system by reading from the second specified one of the snapshot file systems and writing to the production file system, the new snapshot file system keeping a record of data blocks that have been modified by the writing to the production file system, and initiating a background process of copying data blocks from the second specified one of the snapshot file systems to the production file system if the data blocks have not been modified by the writing to the production file system, wherein the process of copying data blocks from the second specified one of the snapshot file systems to the production file system copies the data blocks in at least the save volume supporting the second specified one of the snapshot file systems, each data block in the respective save volume supporting the second specified one of the snapshot file systems being copied to the clone volume if said record of data blocks indicates that said each data block has not yet been modified by the writing to the production file system, and prior to said each data block in the respective save volume supporting the second specified one of the snapshot file systems being copied to the clone volume, the original content of said each data block in the clone volume being copied from the clone volume to a save volume supporting the new snapshot file system.

12. The file server as claimed in claim 11, wherein the file server is programmed for responding to completion of the copying of the background routine by no longer responding to subsequent requests for read access to the production file system by reading from the second specified one of the snapshot file systems and instead responding to subsequent requests for read access to the production file system by reading from the production file system.

13. The file server as claimed in claim 11, wherein the snapshot queue includes a series of save volumes including the save volume supporting the second specified one of the snapshot file systems and all of the save volumes produced after the save volume supporting the second specified one of the snapshot file systems and before the save volume supporting the new snapshot file system, and

wherein the process of copying data blocks from the second specified snapshot file system to the production file system includes, for each data block included in at least one of the save volumes in the series of save volumes, copying said each data block only from the oldest save volume including said each data block, said each data block being copied to the clone volume if said record of data blocks indicates that said each data block has not yet been modified by the writing to the production file system.

14. The file server as claimed in claim 13, wherein said each data block is copied only from the oldest save volume including said each data block by first copying data blocks from the respective save volume supporting the second specified one of the snapshot file systems and recording in a bit map indications of the copied data blocks, and then successively copying additional data blocks from the newer save volumes in the series and recording in the bit map indications of the copied additional data blocks, wherein each additional data block in the newer save volumes in the series is not copied if the bit map indicates that it was already copied from an older save volume.

15. The file server as claimed in claim 11, wherein the snapshot queue includes a series of save volumes including the save volume supporting the second specified one of the snapshot file systems and all of the save volumes produced after the save volume supporting the second specified one of the snapshot file systems and before the save volume supporting the new snapshot file system, and

wherein the process of copying data blocks from the second specified one of the snapshot file systems to the production file system includes copying data blocks from the newest save volume in the series to the production file system, and then successively copying data blocks from the older save volumes in the series to the production file system, each data block being copied to the clone volume if said record of data blocks indicates that said each data block has not yet been modified by the writing to the production file system.

16. A method of operating a data storage system providing access to a production dataset and at least one snapshot dataset, the data storage system including storage containing the production dataset and the snapshot dataset, the snapshot dataset being the state of the production dataset at a point in time when the snapshot dataset was created, wherein the method comprises instantaneous restoration of the production dataset with the state of the snapshot dataset by initiating read/write access through a foreground routine to what appears to be a restored version of the production dataset while the production dataset is being restored by a background routine, the foreground routine keeping a record of data blocks that have been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine, the background routine copying data blocks from the snapshot dataset to the production dataset if said record of the data blocks indicates that the data blocks have not yet been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine.

17. The method as claimed in claim 16 wherein the foreground routine provides read access to the snapshot dataset and write access to the production dataset.

18. The method as claimed in claim 16, which further includes terminating read/write access through the foreground routine when the background routine has finished copying data blocks from the snapshot dataset to the production dataset.

19. The method as claimed in claim 16, which includes deleting the snapshot dataset when the background routine has finished copying data blocks from the snapshot dataset to the production dataset.

20. The method as claimed in claim 16, which includes a process of creating a snapshot copy of the restored production dataset concurrent with the restoration of the production dataset, the process of creating the snapshot copy using the record of data blocks in the production dataset that have been modified, in order to save original content of at least some of the data blocks being modified by the read/write access through the foreground routine.

21. The method as claimed in claim 16, wherein the dataset further includes storage containing a clone volume of data blocks supporting the production dataset and at least one save volume supporting the snapshot dataset, the save volume containing original content of corresponding data blocks in the clone volume existing at a time of creation of the snapshot dataset, and wherein the background routine copies the content of each data block in the save volume to the corresponding data block in the clone volume if the record of data blocks in the production dataset that have been modified indicates that the corresponding data block has not been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine.

22. A method of operating a data storage system for providing access to a production dataset and at least one snapshot dataset, the data storage system including storage containing the production dataset and the snapshot dataset, the snapshot dataset being the state of the production dataset at a point in time when the snapshot dataset was created, said method comprising instantaneous restoration of the production dataset with the state of the snapshot dataset by responding to requests for read/write access to the production dataset by reading from the snapshot dataset and writing to the production dataset, and keeping a record of data blocks that have been modified by said writing to the production dataset, and initiating a process of copying data blocks from the snapshot dataset to the production dataset if said record of the data blocks indicates that the data blocks have not yet been modified by said writing to the production dataset.

23. The method as claimed in claim 22, which includes responding to completion of the process of copying data blocks by no longer responding to subsequent requests for read access to the production dataset by reading from the snapshot dataset and instead responding to subsequent requests for read access to the production dataset by reading from the production dataset.

24. The method as claimed in claim 22, which includes deleting the snapshot dataset when the process of copying data blocks has been completed.

25. The method as claimed in claim 22, which includes performing a process of creating a snapshot copy of the restored production dataset concurrent with the restoration of the production dataset, the process of creating the snapshot copy using said record of data blocks that have been modified, in order to save original content of at least some of the data blocks being modified by said writing to the production dataset.

26. The method as claimed in claim 22, wherein the data storage system further includes storage containing a clone volume of data blocks supporting the production dataset and at least one save volume supporting the snapshot dataset, the save volume containing original content of corresponding data blocks in the clone volume existing at a time of creation of the snapshot dataset, and wherein the background routine copies the content of each data block in the save volume to the corresponding data block in the clone volume if said record of data blocks that have been modified indicates that the corresponding data block has not been modified by said writing to the production dataset.

27. A method of operating a file server for providing access to a production file system and a plurality of snapshot file systems, each of the snapshot file systems being the state of the production file system at a respective point in time when said each of the snapshot file systems was created, the file server including storage containing a clone volume of data blocks supporting the production file system, and the storage containing, for said each of the snapshot file systems, a respective save volume of data blocks supporting said each of the snapshot file systems, the respective save volume of said each of the snapshot file systems containing data blocks having resided in the clone volume at the respective point in time when said each of the snapshot file systems was created, wherein said method comprises:

maintaining the save volumes in a snapshot queue in a chronological order of the respective points in time when the snapshot file systems were created, the save volume supporting the oldest one of the snapshot file systems residing at the head of the snapshot queue, and the save volume supporting the youngest one of the snapshot file systems residing at the tail of the snapshot queue,

performing a read access upon the production file system by reading from the clone volume,

performing a write access upon the production file system by writing to the clone volume but before modifying a block of production file system data in the clone volume, copying the block of production file system data from the clone volume to the save volume at the tail of the snapshot queue if said block of production file system data in the clone volume has not yet been modified since the respective point in time of creation of the snapshot file system supported by the save volume at the tail of the snapshot queue,

performing a read access upon a specified data block of a first specified one of the snapshot file systems by reading from the save volume supporting the first specified one of the snapshot file systems if the specified data block is found in the save volume supporting the first specified one of the file systems, and if the specified data block is not found in the save volume supporting the first specified one of the file systems, searching for the specified data block in a next subsequent save volume in the snapshot queue, and if the specified data block is found in the next subsequent save volume in the snapshot queue, reading the specified data block from the next subsequent save volume in the snapshot queue, and if the specified data block is not found in any subsequent save volume in the snapshot queue, then reading the specified data block from the clone volume;

wherein said method further includes instantaneous restoration of the production file system with the state of a second specified one of the snapshot file systems by creating a new snapshot file system and responding to subsequent requests for access to the production file system by reading from the second specified one of the snapshot file systems and writing to the production file system, the new snapshot file system keeping a record of data blocks that have been modified by the writing to the production file system, and initiating a background process of copying data blocks from the second specified one of the snapshot file systems to the production file system if the data blocks have not been modified by the writing to the production file system, wherein the process of copying data blocks from the second specified one of the snapshot file systems to the production file system copies the data blocks in at least the save volume supporting the second specified one of the snapshot file systems, each data block in the respective save volume supporting the second specified one of the snapshot file systems being copied to the clone volume if said record of data blocks indicates that said each data block has not yet been modified by the writing to the production file system, and prior to said each data block in the respective save volume supporting the second specified one of the snapshot file systems being copied to the clone volume, the original content of said each data block in the clone volume being copied from the clone volume to a save volume supporting the new snapshot file system.

28. The method as claimed in claim 27, which includes responding to completion of the copying of the background routine by no longer responding to subsequent requests for read access to the production file system by reading from the second specified snapshot file system and instead responding to subsequent requests for read access to the production file system by reading from the production file system.

29. The method as claimed in claim 27, wherein the snapshot queue includes a series of save volumes including the save volume supporting the second specified one of the snapshot file systems and all of the save volumes produced after the save volume supporting the second specified one of the snapshot file systems and before the save volume supporting the new snapshot file system, and

wherein the process of copying data blocks from said second specified one of the snapshot file systems to the production file system includes, for each data block included in at least one of the save volumes in the series of save volumes, copying said each data block only from the oldest save volume including said each data block, said each data block being copied to the clone volume if said record of data blocks indicates that said each data block has not yet been modified by the writing to the production file system.

30. The method as claimed in claim 29, wherein said each block is copied only from the oldest save volume including said each data block by first copying data blocks from the respective save volume supporting the second specified one of the snapshot file systems and recording in a bit map indications of the copied data blocks, and then successively copying additional data blocks from the newer save volumes in the series and recording in the bit map indications of the copied additional data blocks, wherein each additional data block in the newer save volumes in the series is not copied if the bit map indicates that it was already copied from an older save volume.

31. The method as claimed in claim 27, wherein the snapshot queue includes a series of save volumes including the save volume supporting the second specified one of the snapshot file systems and all of the save volumes produced after the save volume supporting the second specified one of the snapshot file systems and before the save volume supporting the new snapshot file system, and

wherein the process of copying data blocks from said second specified one of the snapshot file systems to the production file system includes copying data blocks from the newest save volume in the series to the production file system, and then successively copying data blocks from the older save volumes in the series to the production file system, each data block being copied to the clone volume if said record of data blocks indicates that said each block has not yet been modified by the writing to the production file system.