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About reset Change Block Tracking (CBT) for VMware Backups

Created: 19 Feb 2013 • Updated: 21 Feb 2013 | 2 comments
This issue has been solved. See solution.

I found one Symantec KB about reset Change Block Tracking (CBT) for VMware Backups.

One setting is need to edit setting of VM
  • Locate "ctkEnabled" and change the value to "false"
  • Locate "scsi0:x.ctkEnabled" and change the value to false.  (where "x" is the number for the vmdk file, example scsi0:0.ctkEnabled would be the first VMDK for the virtual machine)
  • Open the folder the virtual machine is stored in on the datastore and remove any -CTK.VMDK files
  • Power on the virtual machine
  • After the virtual machine has completed it's boot sequence, power the virtual machine off. Note: This step is required to update the CTK tables for the virtual machine.
  • Power on the virtual machine.
  • Run the backup of the virtual machine.  When this backup runs CBT will get enabled. (If the backup is scheduled to run at a later time CBT will get enabled at that time)

Do I need to change ctkEnabled" and change back the value to "true" after power on VM? When change the value of "ctkEnabled" to "false", do it mean that disable Change Block Tracking (CBT) for VMware Backups? Backup size of each VM is equal to the maximum size of VMDK when each backup performs?

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Gurvinder Rait's picture

Backup Exec article you referred to

this is an article from Veamm -

The CBT will get re-enabled automatically when you rerun the backup of that VM after attempting the steps mentioned.

If CBT is not working then change blocks will not be reported accurately and Backup Exec would backup more data than is used on the vmdk

I hope this answers your query.