When I restarted my System Rollback Rx defraged a number of snapshots. What happened?
Posted by , Last modified by on 27 Sep 2013
The "Defrag Snapshot" process optimizes the snapshots and releases any space on the hard disk that can be released.
Snapshots are organized in a "parent-child" arrangement. Therefore, a "child" snapshot contains, by default, everything in the "parent" plus whatever else is specified in the child. For performance reasons, we do not explicitly copy all parent references into the child, these are implied.
Therefore, when you delete any snapshot, the parent (and all its associated implications) no longer exists. References to certain files in that snapshot have to be moved into the "child". In addition, other file references are no longer required and may be deleted. This is what finally releases the protected disk space back to Windows.
Obviously, this reconciliation involves locking files for a period of time and may have negative performance implications; therefore, this is not done in real time. Instead, the snapshot is "marked" as deleted and control released back to the User.
The actual reconciliation of the snapshots and release of space back to Windows is done by a batch Snapshot Defragmentation process. This Defrag is hard-coded to run automatically after a certain number of snapshots are added or deleted. Because it is resource-heavy, it runs at a background process; if the Snapshot Defrag does not complete, it is automatically run on the next system boot.
You can manually run the Defrag at any time by selecting Advanced Options -> Defrag Snapshots from the menu bar.
If you have any troubles with RollBack Rx, contact Horizon DataSys Technical Support -> "Submit a Ticket"