The present invention discloses a method and system for snapshot-based online backup operations permitting reduced requirements to storage capacity and computational overhead for snapshot function.
At the beginning of an online backup operation, the backup software system creates a snapshot of source data storage. The snapshot includes a watch-list used for identifying blocks of a source storage which are watched by snapshot management means for update. If a block included into the watch-list was requested for update, the snapshot management means preserve original contents of that block in a retention container for the purpose of temporary store. The retention container includes a set of temporal stores dedicated for transient storing of blocks until they are backed up.
The essence of the invention is enabling to exclude blocks from the watch-list and the retention container at any moment within the period of snapshot operation. Therefore it is possible to exclude unnecessary blocks from the scope of blocks managed by the snapshot management means, for the purpose of preserving point-in-time data.
Backed up blocks can be operatively excluded from the snapshot so that unchanged blocks are excluded from the watch-list and updated blocks are removed from the retention container. In the latter case temporal stores are shrunk as well. This technique allows to reduce progressively storage expenses and computational overheads required for maintenance of a snapshot being used in the online backup routine.
When a volume-level online backup is performed the snapshot is switched to the read-once mode at the beginning of the data copying stage. A backup utility performs sequential read of blocks from the snapshot. The snapshot management means automatically exclude requested blocks from the scope of managed blocks.