Circular and bi-directional mirroring of flexible volumes

• US 7,467,169 B2
• Filed: 10/31/2005
• Issued: 12/16/2008
• Est. Priority Date: 10/31/2005
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: Network Appliance Incorporated (NetApp, Inc.)
• Inventors: Gole, Abhijeet, Hamilton, Eric
• Primary Examiner(s): Alam; Hosain T
• Assistant Examiner(s): CHEEMA, AZAM M
• Application Number:
  US11/264,685
• Publication Number:
  US 20070100910A1
• Time in Patent Office: 1,142 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/2074 Asynchronous techniques
• CPC Class Codes: G06F 11/2079 Bidirectional techniques
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

A method and system mirror flexible volumes in a circular or bi-directional configuration, without creating a deadlock. A source filer maintains a number of log files on a destination filer, where the number of log files is greater than or equal to the number of cache flush operations the primary filer performs between cache flush operations on the destination filer. The source filer can create the log files in advance. Alternatively or in addition, the source filer can create the log files as needed, i.e., the source filer can create a log file when the source filer flushes its cache. Once the destination filer flushes its cache, the log files created prior to the destination filer cache flush can be deallocated or reused.

Claims

1. A method of mirroring data, comprising the steps of:

in a first receiving step, receiving, at least one data write request at a source storage server;

storing, in a first cache on said source storage server, said at least one data write request received in said first receiving step;

writing, by said source storage server into at least one first log file of a plurality of log files on a destination storage server, information about said at least one data write request received in said first receiving step;

in at least one cache flush operation performed on said source storage server, flushing said first cache on said source storage server, and, responsive to receiving at least one next data write request at said source storage server, beginning to write information about said at least one next data write request into at least one second log file of said plurality of log files on said destination storage server by said source storage server,

wherein, each time said first cache is flushed, said source storage server begins writing information about at least one next data write request to a different one of said plurality of log files on said destination storage server;

in a second receiving step, receiving at least one data write request at said destination storage server;

storing, in a second cache on said destination storage server, said at least one data write request received in said second receiving step;

in at least one cache flush operation performed on said destination storage server, flushing said second cache on said destination storage server; and

responsive to said flushing of said second cache, performing one of deallocating and overwriting said at least one first log file,

wherein a total number of said plurality of log files on said destination storage server is greater than or equal to a number of cache flush operations performed on said source storage server between cache flush operations performed on said destination storage server.

2. The method of claim 1, further comprising pre-allocating at least three log files on said destination storage server.

3. The method of claim 1, wherein flushing the first cache on said source storage server comprises allocating an additional log file on said destination storage server.

4. The method of claim 1, further comprising:

calculating a desired number of log files, based on a number of times the first cache on the source storage server is flushed and on a number of times the second cache on the destination storage server is flushed; and

if the calculated desired number of log files is less than the total number of said plurality of log files on said destination storage server, deleting at least one of the plurality log files on said destination storage server.

5. The method of claim 1, further comprising:

calculating a desired number of log files, based on a number of times the first cache on the source storage server is flushed and on a number of times the second cache on the destination storage server is flushed; and

if the calculated desired number of log files is greater than the total number of said plurality of log files on said destination storage server, creating at least one additional log file on said destination storage server.

6. The method of claim 1, further comprising, after receiving the at least one data write request in said first receiving step, storing information about the at least one data write request in a non-volatile memory.

7. A method of mirroring data, comprising the steps of:

in a first receiving step, receiving, at least one data write request at a source storage server;

storing, in a first cache on said source storage server, said at least one data write request received in said first receiving step;

writing, by said source storage server into at least one first log file of a plurality of log files on a destination storage server, information about said at least one data write request received in said first receiving step;

in at least one cache flush operation performed on said source storage server, flushing said first cache on said source storage server, and, responsive to receiving at least one next data write request at said source storage server, beginning to write information about said at least one next data write request into at least one second log file of said plurality of log files on said destination storage server by said source storage server,

wherein, each time said first cache is flushed, said source storage server begins writing information about at least one next data write request to a different one of said plurality of log files on said destination storage server;

in a second receiving step, receiving at least one data write request at said destination storage server;

storing, in a second cache on said destination storage server, said at least one data write request received in said second receiving step;

in at least one cache flush operation performed on said destination storage server, flushing said second cache on said destination storage server; and

responsive to said flushing of said second cache, de allocating said at least one first log file,

wherein a total number of said plurality of log files on said destination storage server is greater than or equal to a number of cache flush operations performed on said source storage server between cache flush operations performed on said destination storage server.

8. The method of claim 7, further comprising, after said second cache is flushed, beginning to write information about yet subsequently received data write requests on another log file.

9. The method of claim 8, wherein beginning to write information about yet subsequently received data write requests comprises allocating the another log file.

10. A system for mirroring data, comprising:

a source storage server including a first cache; and

a destination storage server including a second cache, said destination storage server being operative to maintain a plurality of log files including at least one first log file and at least one second log file,

wherein said source storage server is operative;

to receive at least one first data write request;

to store the at least one first data write request in the first cache;

to write information about the at least one first data write request into the at least one first log file maintained on said destination storage server; and

in at least one cache flush operation, to flush the first cache, and, responsive to receiving at least one next data write request at said source storage server, to begin to write information about said at least one next data write request into the at least one second log file maintained on said destination storage server,

wherein, each time the first cache is flushed, said source storage server is operative to begin writing information about at least one next data write request to a different one of said plurality of log files on said destination storage server,

wherein said destination storage server is operative;

to receive at least one second data write request;

to store the at least one second data write request in the second cache;

in at least one cache flush operation, to flush the second cache, and

responsive to said flushing of said second cache, to perform one of de allocating and overwriting the at least one first log file,

wherein a total number of said plurality of log files on said destination storage server is greater than or equal to a number of cache flush operations performed by said source storage server between cache flush operations performed by said destination storage server.

11. The system of claim 10, wherein said destination storage server is further operative to maintain a third log file.

12. The system of claim 10, wherein said source storage server is further operative to allocate an additional log file on said destination storage server.

13. The system of claim 10, wherein said source storage server is further operative to calculate a desired number of log files, based on a number of times the first cache on said source storage server is flushed and on a number of times the second cache on said destination storage server is flushed.

14. The system of claim 13, wherein said source storage server is operative, if the calculated desired number of log files is less than the total number of said plurality of log files maintained on said destination storage server, to delete at least one of the plurality of log files maintained on said destination storage server.

15. The system of claim 13, wherein said source storage server is operative, if the calculated desired number of log files is greater than the total number of said plurality of log files maintained on said destination storage server, to create at least one additional log file on said destination storage server.

16. The system of claim 10, wherein said source storage server is further operative, after the second cache on said destination storage server is flushed, to begin to write information about yet subsequently received write requests on another log file.

17. The system of claim 16, wherein said source storage server is further operative, after the second cache on said destination storage server is flushed, to allocate the another log file before beginning to write information about the subsequently received write requests on the another log file.

18. The system of claim 10, wherein said source storage server comprises a non-volatile memory, and wherein said source storage server is further operative, after receiving the at least one first data write request, to store information about the at least one first data write request in the non-volatile memory.