VMware vSphere 5.1, iSCSI block storage, old backup solution uses Changed Block Tracking (CBT) for incremental backups. New backup solution also uses Changed Block Tracking (CBT), but the current CBT info pertains to the old backup solution as the new backup solution didn't actually run a backup yet.

Does CBT need to be reset in order for the new backup solution to start with a clean slate? Resetting CBT for good measure isn't an option since downtime needs to be scheduled to reset CBT. Shutting VM down, and then restarting twice is required to reset CBT.

1 Answer 1


No, you don't need to do that. CBT is based on incrementing a generation counter. If you do the first backup with the new software then it will have nothing to compare to, that means it will create a full backup and increment the counter. And the second and subsequent backups with the new software will create a correct delta backup of changed blocks.


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