Recovery of file system data in file servers mirrored file system volumes

• US 20040153736A1
• Filed: 11/21/2003
• Published: 08/05/2004
• Est. Priority Date: 10/04/2000
• Status: Active Grant

• Current Assignee: Network Appliance Incorporated (NetApp, Inc.)
• Original Assignee: Network Appliance Incorporated (NetApp, Inc.)
• Inventors: Kleiman, Steven R., Viswanathan, Srinivasan
• Granted Patent: US 7,096,379 B2
• Time in Patent Office: Days
• US Class Current: 714/6
• 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: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

The invention provides a method and system for recovery of file system data in file servers having mirrored file system volumes. The invention makes use of a “snapshot” feature of a robust file system (the “WAFL File System”) disclosed in the Incorporated Disclosures, to rapidly determined which of two or more mirrored volumes is most up-to-date, and which file blocks of the most recent mirrored volume have been changed from each one of the mirrored file systems. In a preferred embodiment, among a plurality of mirrored volumes, the invention rapidly determines which is the most up-to-date by examining a consistency point number maintained by the WAFL File System at each mirrored volume. The invention rapidly pairwise determines what blocks are shared between that most up-to-date mirrored volume and each other mirrored volume, in response to a snapshot of the file system maintained at each mirrored volume and are stored in common pairwise between each mirrored volume and the most up-to-date mirrored volume. The invention re synchronizes only those blocks that have been changed between the common snapshot and the most up-to-date snapshot.

Claims

1. A method, including steps of

examining a plurality of mirrored file system volumes for a consistency point value;

determining a most up-to-date said file system volume in response to said steps of examining; and

selecting a set of changed file blocks between said up-to-date said file system and each one of said plurality of mirrored file system volumes.

2. A method as in claim 1, wherein said steps of selecting include

determining a snapshot held in common between said most up-to-date said file system volume and at least one of said plurality of mirrored file system volumes;

and

selecting those file blocks changed between said snapshot held in common and said up-to-date said file system volume.

3. A method as in claim 1 or 2, including steps of re-synchronizing at least one of said plurality of mirrored file system volumes in response to said steps of selecting.

4. Apparatus including

a plurality of mirrored file system volumes, each having at least one snapshot including an entire consistent file system, each said snapshot having a consistency point value;

a first comparison element capable of being coupled to a plurality of said consistency point values;

a second comparison element, responsive to an output of said first comparison element, said second comparison element being capable of being coupled (a) to a first snapshot associated with said output on a first said volume and (b) to a second snapshot associated with a second said volume, said second comparison element being capable of providing a selection of file blocks in response thereto.

5. Apparatus as in claim 4, wherein said second snapshot is held in common between said first volume and said second volume.

6. Apparatus as in claim 4 or 5, including an element capable of resynchronizing at least one of said plurality of mirrored file system volumes in response to said second comparison element.