SUMMARY

CBT drive on a Hyper-V cluster can get out of sync.  This can cause CBT issues with getting changed blocks resulting in incremental backups that are the same size of a full backup.

ISSUE

----- Error Messages -----
CBTDriverError:uvbCbtSnapshotCreationStarted:: FFFFFFFF80070002
Due to previous error, Unitrends agent is not able to use the Hyper-V CBT filter driver during backup job for VM {A4C9989D-86C9-4769-81FE-E8765E5B6691}: all files will be backed up as full not change blocks.
----- End Error Messages -----

RESOLUTION

Open the following file in notepad and review the Sync Status line on each Hyper-V node in the cluster.

C:\unicbt\config\in.xml

You will see if the drive is InSync or NoSync or OutSync like the following.

<CBT>
  <VERSION>2</VERSION>
  <SYNC_STATUS>NoSync</SYNC_STATUS>

If the driver is out of sync you will want to stop the CBT (UnitrendSVC) service on each Hyper-V node.



Once the UnitrendSVC service is stopped on each node, start the UnitrendSVC on each node to complete the sync CBT. 


Perform an Inventory Sync. This pulls the most current inventory to update our database. Lastly, take another Hyper-V full backup which, once completed, should remedy the incremental backup size issues moving forward.

CAUSE

CBT drive loses sync with the other cluster nodes which requires a reset to get the driver back in sync.