MIRRORING DATA BETWEEN PRIMARY AND SECONDARY SITES

• US 20070288710A1
• Filed: 06/08/2006
• Published: 12/13/2007
• Est. Priority Date: 06/08/2006
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Boyd, Kenneth Wayne, Dewey, Douglas William, Day, Kenneth Fairclough
• Granted Patent: US 7,877,628 B2
• Time in Patent Office: Days
• US Class Current: 711/162
• CPC Class Codes: G06F 11/2069 Management of state, configuration or failover
• CPC Class Codes: G06F 11/2071 using a plurality of controllers
• CPC Class Codes: G06F 11/2082 Data synchronisation

Abstract

Provided are a method, system, and article of manufacture for mirroring data between a first site and a second site. Updates to segments of storage at the first site are copied to corresponding segments of storage at the second site. Codes are generated from the segments at the second site and a valid flag is provided for at least one code indicating whether the code for the segment of data is valid. One code is generated from each segment of storage at the first site. An operation is initiated to copy segments from the second site to the first site. A determination is made for segments at the second site as to whether the valid flag for the code for the segment at the second site indicates that the code is valid in response to initiating the copy operation. The valid code for at least one segment in the second site is compared with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site as part of the copy operation.

Claims

1. A method for synchronizing data between a first site and a second site, comprising:

copying updates to segments of storage at the first site to corresponding segments of storage at the second site;

providing codes generated from the segments at the second site and a valid flag for at least one code indicating whether the code for the segment of data is valid;

providing codes generated from segments of storage at the first site;

initiating an operation to copy segments from the second site to the first site;

determining, for segments at the second site, whether the valid flag for the code for the segment at the second site indicates that the code is valid in response to initiating the copy operation; and

comparing the valid code for at least one of the segments in the second site with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site as part of the copy operation.

2. The method of claim 1, further comprising:

providing valid flags for codes generated from segments at the first site, wherein the code for at least one segment in the second site is compared with the code for the corresponding segment at the first site if the valid flags for the corresponding segments at the first and second sites indicate valid.

3. The method of claim 1, further comprising:

generating a new code for each segment whose valid flag indicates that the segment is invalid from current data for the segment; and

comparing the new code for the segment at the second site with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site.

4. The method of claim 1, further comprising:

copying data from the second site to the first site if the codes do not match.

6. The method of claim 1, further comprising:

receiving an update to one segment at the second storage site;

setting the valid flag for the segment for which the update is received to indicate that the code is invalid;

calculating a new code for one segment whose valid flag is invalid; and

setting the valid flag for the segment for which the new code is calculated to indicate that the code for the segment is valid.

7. The method of claim 6, wherein the received update is stored in a cache, further comprising:

destaging updates for one segment from the cache to the second site storage, wherein the new code is calculated for one segment in response to destaging the updates for the segment.

8. The method of claim 7, further comprising:

determining whether the cache includes a previous update for the block to which the received update applies; and

writing the received update to the block in cache to overwrite any previous update to the block in the cache, wherein the valid flag for the segment is only set to indicate that the code is invalid in response to determining that there is no previous update for the block in the cache.

9. The method of claim 7, further comprising:

staging one segment at the second site into the cache in response to receiving an update to a block in the segment, wherein updated and unchanged portions of the segment are in the cache, and wherein the new code is calculated from the entire segment stored in the cache in response to destaging the segment.

10. The method of claim 6, wherein the received update is stored in a cache, further comprising:

destaging updates for one segment from the cache to the first site storage; and

initiating a background operation to calculate a new code for each segment whose valid flag indicates that the code is invalid.

5. The method of 4, further comprising

copying data from the first site to the second site while the first site is receiving updates;

receiving updates at the second site in response to detecting a failure at the first site, wherein updates are not received at the first site while updates are being received at the second site; and

detecting an availability of the first site after the failure at the first site, wherein the copy operation is initiated in response to detecting the availability of the first.

11. A method for synchronizing data between a first site and a second site, comprising:

copying data from segments of storage at the first site to corresponding segments of storage at the second site;

receiving updates at the second site in response to detecting a failure at the first site, wherein updates are not received at the first site while updates are being received at the second site;

detecting an availability of the first site before the first site is ready to begin receiving updates and mirroring updates to the second site;

initiating operations to calculate codes for the segments at the first and second sites in response to detecting the availability of the first site;

initiating a synchronize operation to copy segments from the second site to the first site in response to determining that the first site is ready to begin receiving updates and mirror updates to the second site; and

comparing the codes for segments in the second site with the codes for the corresponding segments at the first site to determine whether to copy the data from the segments at the second site to the first site as part of the synchronize operation.

12. The method of claim 11, further comprising:

restoring at least one of the segments to the first site from a backup device in response to detecting the availability of the first site, wherein the operations to calculate the code are initiated while segments are being restored from the backup device.

13. A system for synchronizing data between a first site and a second site, comprising:

a first system managing access to the first site;

a first copy manager program executed by the first system to perform operations comprising;

copying updates to segments of storage at the first site to corresponding segments of storage at the second site; and

providing codes generated from the segments of storage at the first site;

a second system managing access to the second site; and

a second copy manager program executed by the second system to perform operations comprising;

providing codes generated from the segments at the second site and a valid flag for at least one code indicating whether the code for the segment of data is valid;

initiating an operation to copy segments from the second site to the first site;

determining, for segments at the second site, whether the valid flag for the code for the segment at the second site indicates that the code is valid in response to initiating the copy operation; and

comparing the valid code for at least one of the segments in the second site with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site as part of the copy operation.

14. The system of claim 13, wherein the first copy manager is executed to further provide valid flags for codes generated from segments at the first site, wherein the code for at least one segment in the second site is compared with the code for the corresponding segment at the first site if the valid flags for the corresponding segments at the first and second sites are valid.

15. The system of claim 13, wherein the first and second copy managers further generate a new code for each segment whose valid flag indicates that the segment is invalid from current data for the segment, and wherein the second copy manager further compares the new code for the segment at the second site with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site.

16. The system of claim 13, wherein the second copy manager further copies data from the second site to the first site if the codes do not match.

17. The system of claim 13, wherein the second copy manager further performs:

receiving an update to one segment at the second storage site;

setting the valid flag for the segment for which the update is received to indicate that the code is invalid;

calculating a new code for one segment whose valid flag is invalid; and

setting the valid flag for the segment for which the new code is calculated to indicate that the code for the segment is valid.

18. The system of claim 17, further comprising:

a cache in the second system, wherein the received updates at the second system are stored in the cache, wherein the second copy manager further destages updates for one segment from the cache to the second site storage, wherein the second copy manager calculates the new code for one segment in response to destaging the updates for the segment.

19. A system for synchronizing data between a first site and a second site, comprising:

a first system managing access to the first site;

a second system managing access to the second site;

a first copy manager executed by the first system and a second copy manager executed by the second system, wherein at least one of the first and second copy managers are executed to perform operations, the operations comprising;

copying data from segments of storage at the first site to corresponding segments of storage at the second site;

receiving updates at the second site in response to detecting a failure at the first site, wherein updates are not received at the first site while updates are being received at the second site;

detecting an availability of the first site before the first site is ready to begin receiving updates and mirroring updates to the second site;

initiating operations to calculate codes for the segments at the first and second sites in response to detecting the availability of the first site;

initiating a synchronize operation to copy segments from the second site to the first site in response to determining that the first site is ready to begin receiving updates and mirror updates to the second site; and

comparing the codes for segments in the second site with the codes for the corresponding segments at the first site to determine whether to copy the data from the segments at the second site to the first site as part of the synchronize operation.

20. The system of claim 19, wherein the operations further comprise:

restoring at least one of the segments to the first site from a backup device in response to detecting the availability of the first site, wherein the operations to calculate the code are initiated while segments are being restored from the backup device.

21. An article of manufacture including program illogic implemented in a first and second copy managers for synchronizing data between a first site and a second site, wherein at least one of the first and second copy mangers are executed to perform operations, the operations comprising:

copying updates to segments of storage at the first site to corresponding segments of storage at the second site;

providing codes generated from the segments at the second site and a valid flag for at least one code indicating whether the code for the segment of data is valid;

providing codes generated from segments of storage at the first site;

initiating an operation to copy segments from the second site to the first site;

determining, for segments at the second site, whether the valid flag for the code for the segment at the second site indicates that the code is valid in response to initiating the copy operation; and

comparing the valid code for at least one of the segments in the second site with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site as part of the copy operation.

22. The article of manufacture of claim 21, wherein the operations further comprise:

providing valid flags for codes generated from segments at the first site, wherein the code for at least one of the segments in the second site is compared with the code for the corresponding segment at the first site if the valid flags for the corresponding segments at the first and second sites indicate valid.

23. The article of manufacture of claim 21, wherein the operations further comprise:

generating a new code for each segment whose valid flag indicates that the segment is invalid from current data for the segment; and

comparing the new code for the segment at the second site with the code for the corresponding segment at the first site to determine whether to copy the data from the segment at the second site to the first site.

24. The article of manufacture of claim 21, wherein the operations further comprise:

copying data from the second site to the first site if the codes do not match.

25. The article of manufacture of claim 24, wherein the operations further comprise

copying data from the first site to the second site while the first site is receiving updates;

receiving updates at the second site in response to detecting a failure at the first site, wherein updates are not received at the first site while updates are being received at the second site; and

detecting an availability of the first site after the failure at the first site, wherein the copy operation is initiated in response to detecting the availability of the first.

26. The article of manufacture of claim 21, wherein the operations further comprise:

receiving an update to one segment at the second storage site;

setting the valid flag for the segment for which the update is received to indicate that the code is invalid;

calculating a new code for one segment whose valid flag is invalid; and

setting the valid flag for the segment for which the new code is calculated to indicate that the code for the segment is valid.

27. The article of manufacture of claim 26, wherein the received update is stored in a cache, wherein the operations further comprise:

destaging updates for one segment from the cache to the second site storage, wherein the new code is calculated for one segment in response to destaging the updates for the segment.

28. The article of manufacture of claim 27, wherein the operations further comprise:

determining whether the cache includes a previous update for the block to which the received update applies; and

writing the received update to the block in cache to overwrite any previous update to the block in the cache, wherein the valid flag for the segment is only set to indicate that the code is invalid in response to determining that there is no previous update for the block in the cache.

29. The article of manufacture of claim 27, wherein the operations further comprise:

staging one segment at the second site into the cache in response to receiving an update to a block in the segment, wherein updated and unchanged portions of the segment are in the cache, and wherein the new code is calculated from the entire segment stored in the cache in response to destaging the segment.

30. The article of manufacture of claim 26, wherein the received update is stored in a cache, wherein the operations further comprise:

destaging updates for one segment from the cache to the first site storage; and

initiating a background operation to calculate a new code for each segment whose valid flag indicates that the code is invalid.

31. An article of manufacture including code implemented in a first and second copy managers for synchronizing data between a first site and a second site, wherein at least one of the first and second copy mangers are executed to perform operations, the operations comprising:

copying data segments of storage at the first site to corresponding segments of storage at the second site;

receiving updates at the second site in response to detecting a failure at the first site, wherein updates are not received at the first site while updates are being received at the second site;

detecting an availability of the first site before the first site is ready to begin receiving updates and mirroring updates to the second site;

initiating operations to calculate codes for the segments at the first and second sites in response to detecting the availability of the first site;

initiating a synchronize operation to copy segments from the second site to the first site in response to determining that the first site is ready to begin receiving updates and mirror updates to the second site; and

comparing the codes for segments in the second site with the codes for the corresponding segments at the first site to determine whether to copy the data from the segments at the second site to the first site as part of the synchronize operation.

32. The article of manufacture of claim 31, wherein the operations further comprise:

restoring at least one of the segments to the first site from a backup device in response to detecting the availability of the first site, wherein the operations to calculate the code are initiated while segments are being restored from the backup device.