METHOD AND SYSTEM FOR RESTORING A VOLUME IN A CONTINUOUS DATA PROTECTION SYSTEM

• US 20080147756A1
• Filed: 02/29/2008
• Published: 06/19/2008
• Est. Priority Date: 02/04/2004
• Status: Active Grant

• Current Assignee: NetApp, Inc.
• Original Assignee: Network Appliance Incorporated (NetApp, Inc.)
• Inventors: Chang, Yafen Peggy, Johnston, Craig Anthony, Trimmer, Donald Alvin, Stager, Roger Keith, Johnson, Randall, Saxena, Pawan, Blaser, Rico
• Granted Patent: US 7,979,654 B2
• Time in Patent Office: Days
• US Class Current: 707/204
• CPC Class Codes: G06F 11/2074 Asynchronous techniques
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G06F 2201/855 Details of asynchronous mirroring using a journal to transfer not-yet-mirrored changes

Abstract

A system for synchronizing a secondary volume with a primary volume in a continuous data protection system includes scanning means for scanning a region of the primary volume; comparing means for comparing the scanned region with a corresponding region of the secondary volume; storing means for storing an identification of the scanned region in a compare delta map when the comparing means returns a discrepancy between the scanned region and the corresponding region; copying means for copying data from the primary volume to the secondary volume, using the compare delta map as a guide to locate the data to copy; and revising means for revising the compare delta map by removing any changes made to the primary volume during a scan interval, which is a period of time required to scan the primary volume.

Claims

1. A system for synchronizing a secondary volume with a primary volume in a continuous data protection system, comprising:

scanning means for scanning a region of the primary volume;

comparing means for comparing said scanned region with a corresponding region of the secondary volume;

storing means for storing an identification of said scanned region in a compare delta map when said comparing means returns a discrepancy between said scanned region and said corresponding region;

copying means for copying data from the primary volume to the secondary volume, using said compare delta map as a guide to locate the data to copy; and

revising means for revising said compare delta map by removing any changes made to the primary volume during a scan interval, which is a period of time required to scan the primary volume.

2. The system according to claim 1, wherein said scanning means scans all regions of the primary volume.

3. The system according to claim 1, further comprising:

a present delta map, covering the changes made to the primary volume from the time of a previous delta map in a delta map chain to the time said scanning means was first activated; and

a point in time (PIT) map, based upon said present delta map.

4. The system according to claim 3, wherein said comparing means uses said PIT map to determine which region of the secondary volume is compared to said scanned region of the primary volume.

5. The system according to claim 1, further comprising:

a dirty region log, wherein only those regions of the primary volume that are listed in said dirty region log are accessed by said scanning means and said comparing means.

6. The system according to claim 5, wherein said dirty region log includes only the regions of the primary volume that have been modified but not yet committed to the secondary volume.

7. The system according to claim 1, wherein said revising means includes:

a scan delta map, including the changes made to the primary volume during said scan interval; and

subtracting means for subtracting the entries in said scan delta map from said compare delta map.

8. The system according to claim 1, wherein said copying means uses said revised compare delta map as a guide to locate the data to copy.

9. The system according to claim 1, further comprising:

a host change delta map, including any changes made to the primary volume during a copy interval, which is a period of time required by said copying means to complete copying data from the primary volume to the secondary volume;

merging means for merging said revised compare delta map into said host change delta map, to create a fix-up delta map; and

inserting means for inserting said fix-up delta map into the end of a delta map chain.

10. The system according to claim 1, further comprising:

selecting means for selecting a delta map in said delta map chain;

marking means for marking said selected delta map as suspect;

adjusting means for adjusting said revised compare delta map by subtracting the changes contained in said selected delta map; and

wherein said selecting means selects the first delta map prior to the start of said scan interval and then selects previous delta maps in said delta map chain until said revised compare delta map is empty.

11. A system for restoring a primary volume from a secondary volume in a continuous data protection system, comprising:

at least one snapshot of the primary volume, each of said at least one snapshots corresponding to a different point in time;

selecting means for selecting one of said at least one snapshots to be restored; and

loading means for loading said selected snapshot from the secondary volume to the primary volume.