06993539 is referenced by 183 patents and cites 21 patents.

A system and method for remote asynchronous replication or mirroring of changes in a source file system snapshot in a destination replica file system using a scan (via a scanner) of the blocks that make up two versions of a snapshot of the source file system, which identifies changed blocks in the respective snapshot files based upon differences in volume block numbers identified in a scan of the logical file block index of each snapshot. Trees of blocks associated with the files are traversed, bypassing unchanged pointers between versions and walking down to identify the changes in the hierarchy of the tree. These changes are transmitted to the destination mirror or replicated snapshot. This technique allows regular files, directories, inodes and any other hierarchical structure to be efficiently scanned to determine differences between versions thereof. The changes in the files and directories are transmitted over the network for update of the replicated destination snapshot in an asynchronous (lazy write) manner. The changes are described in an extensible, system-independent data stream format layered under a network transport protocol. At the destination, source changes are used to update the destination snapshot. Any deleted or modified inodes already on the destination are moved to a temporary or “purgatory” directory and, if reused, are relinked to the rebuilt replicated snapshot directory. The source file system snapshots can be representative of a volume sub-organization, such as a qtree.

Title
System and method for determining changes in two snapshots and for transmitting changes to destination snapshot
Application Number
10/100967
Publication Number
6993539 (B2)
Application Date
March 19, 2002
Publication Date
January 31, 2006
Inventor
Steven R Kleiman
Los Altos
CA, US
Stephen L Manley
London
GB
Shane S Owara
Mountain View
CA, US
Michael L Federwisch
San Jose
CA, US
Agent
Cesari and McKenna
Assignee
Network Appliance
CA, US
IPC
G06R 17/30
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