VEAgent backups of thick provisioned disks and CBT backs up the whole disk

  • KM03095661
  • 15-Feb-2018
  • 15-Feb-2018

This document has not been formally reviewed for accuracy and is provided "as is" for your convenience.


Running a full back of thick provisioned disk with CBT enabled will back up the whole disk with the free space although CBT is enabled.


The behavior of VEAgent backups of thick provisioned disks with CBT enabled seems to be not what is described in the Integration Guide:

"During full backups, only active blocks on the disk are backed up, and unallocated blocks are ignored. This makes the backups space-efficient and faster.
When changed block tracking is enabled, a virtual machine's performance is slightly impacted, but this is small relative to what you gain.
If it is enabled within VMware vSphere, Data Protector will use it.
You can also enable it using the Data Protector GUI, if required."
However, during a full VEAgent backups of a 1.5 TB VM with thick provisioned disks and 400 GB actually occupied we write 1.5 TB to the backup device although CBT is enabled.


If the provisioning is set to thick (although DP does not recognize if the disk is thin or thick) the full backup with CBT will also back up the free space.  This is normal behaviour.
This is also confirmed by VMware in the information about CBT:

CBT should work for incremental/differential backups.