Resynchronization of a target volume with a source volume

• US 6,668,264 B1
• Filed: 04/03/2001
• Issued: 12/23/2003
• Est. Priority Date: 04/03/2001
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: Network Appliance Incorporated (NetApp, Inc.)
• Inventors: Federwisch, Michael, Patterson, Hugo
• Primary Examiner(s): Corrielus, Jean M.
• Application Number:
  US09/825,855
• Time in Patent Office: 994 Days
• Field of Search: 707/202, 707/204, 707/205, 707/10, 707/3, 707/203
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/2064 while ensuring consistency
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: Y10S 707/99936 Pattern matching access
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99956 File allocation

Abstract

An improved method and apparatus for quickly and efficiently updating the original source volume and original target volumes after the original source volume has become temporarily unavailable. The original target volume is characterized as a source volume while the original source volume is temporarily unavailable. Transfer lists of different data blocks are generated. Data blocks not originally found on a source are copied to the target. Data blocks included on a target that were not found on the source are removed. By focusing upon specific data blocks, this technique avoids the use of filer overhead and other computational resources that would be expended if the entire volume were recopied.

Claims

1. A method for aligning a target volume and a source volume after said source volume has been written to, including

comparing information about a set of snapshots associated with said source volume with information about a set of snapshots associated with said target volume to determine common information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common;

reverting said target volume back to a state associated with said common information; and

transferring a set of data blocks from said source volume to said target volume based upon a result of said comparison, so as to align said target volume with said source volume.

2. A method as in claim 1, wherein said step of comparing includes

reading a set of data blocks included in said set of snapshots associated with said source volume; and

reading a set of data blocks included in said set of snapshots associated with said target volume.

3. A method as in claim 1, wherein said step of transferring includes writing data associated with said source volume to said target volume.

4. A method as in claim 1, also including

saving said information about said set of snapshots associated with said target volume, wherein said information concerns an initial state of said target volume prior to said step of transferring.

5. A method as in claim 1, wherein said common information is a most recent information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common.

6. A method as in claim 5, wherein said state to which said target volume is reverted back is a stale associated with said most recent information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common.

7. A method as in claim 1, wherein said step of transferring includes generating a transfer list of data blocks included in said source volume that are not included in said target volume.

8. A method as in claim 7, wherein said transfer list is based upon a union of all data blocks associated with said source volume and a most recent common snapshot.

9. A method as in claim 1, wherein said source volume may receive reads and writes from a client during said set of comparing.

10. A method as in claim 1, wherein said step of comparing is performed by a set of logic coupled to both said source volume and said target volume.

11. A method as in claim 1 also including

generating an alarm to inform a user that data associated with said target volume may be lost.

12. A method for aligning a target volume and a source volume after said source volume has been written to, including

comparing information about a set of snapshots associated with said source volume with information about a set of snapshots associated with said target volume to determine common information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common;

reverting said target volume back to a state associated with said common information;

transferring a set of data blocks from said source volume to said target volume based upon a result of said comparison; and

removing a set of data blocks from a target volume based upon a second result associated with said comparison.

13. A method as in claim 12, also including

saving said information about said set of snapshots associated with said target volume, wherein said information concerns an initial state of said target volume prior to said step of transferring.

14. A method as in claim 12, wherein said common information is a most recent information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common.

15. A method as in claim 14, wherein said state to which said target volume is reverted back is a state associated with said most recent information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common.

16. A method as in claim 12, wherein said step of transferring includes generating a transfer list of data blocks included in said source volume that are not included in said target volume.

17. A method as in claim 16, wherein said transfer list is based upon a union of all data blocks associated with said source volume and a most recent common snapshot.

18. A method as in claim 12, wherein said source volume may receive reads and writes from a client during said set of comparing.

19. A method as in claim 12, wherein said step of comparing is performed by a set of logic coupled to both said source volume and said target volume.

20. A method as in claim 12, wherein said step of removing includes removing a set of blocks included in said target volume that are not included in said source volume.

21. A method as in claim 12, also including

generating an alarm to inform a user that data associated with said target volume may be lost.

22. An apparatus, including a processor, a memory and a set of instructions for aligning a target volume and a source volume after said source volume has been written to, including

an instruction to compare information about a set of snapshots associated with said source volume with information about a set of snapshots associated with said target volume to determine common information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common;

an instruction to revert said target volume back to a state associated with said common information; and

an instruction to transfer a set of data blocks from said source volume to said target volume based upon a result of said comparison.

23. An apparatus as in claim 22, wherein said set of instructions include

an instruction to save said information about said set of snapshots associated with said target volume, wherein said information concerns an initial state of said target volume.

24. An apparatus as in claim 22, wherein said common information is a most recent information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common.

25. An apparatus as in claim 24, wherein said state to which said target volume is reverted back is a state associated with said most recent information that said set of snapshots associated with said target volume and said set of snapshot associated with said source volume share in common.

26. An apparatus as in claim 22, wherein said set of instructions includes

an instruction to generate a transfer list of data blocks included in said source volume that are not included in said target volume.

27. An apparatus as in claim 26, wherein said transfer list is based upon a union of all data blocks associated with said source volume and a most recent common snapshot.

28. An apparatus as in claim 22, wherein said set of instructions includes

an instruction to generate an alarm to inform a user that data associated with said target volume may be lost.