Rollback snapshot defragmenter has two subroutines, the defrag in Rollback application console (in Windows) and the defrag in Rollback subsystem console (in the preboot environment).

The two defrags are almost identical. The one in Windows is hard-coded to automatically defrag snapshots after taking or deleting 'X' number of snapshots (you can see defragging logs in the Event logs), but the defrag in Windows has a pre-condition that is the PC is not busy (no mouse movements or high CPU usage). Because the defrag needs to have a lock of the hard disk for a few seconds, it could slow down the PC. If a user is in the middle of something, they might not like that.  And because of this pre-condition, the defrag in Windows might not have a chance to run properly.

Therefore, we implemented the defrag in the pre-Windows subsystem.  You can turn the subsystem defrag off by unchecking those settings in the program settings -> Advanced Settings. In addition you can manually run the defrag in the subsystem of RollBack Rx from Advanced options->Defrag snapshots.