KB ID : 105017
Products :
Published : March 25, 2016
Created : March 25, 2016
Last Modified : July 18, 2018


VMware backup will fail with the error message "Unable to retrieve queryChangedDiskAreas even after CBT query retry " if the agent is not able to track Changed Blocks of a VM.

There are several scenarios for this issue to occur:

  • If another application accessed the VMs CBT, then this might cause the tracking key that is maintained by the Vembu VMBackup to be broken and when Vembu VMBackup tries to find the CBT, it will fail to retrieve the CBT.

  • If another application has accessed the VM’s CBT and tries to disable and enable the CBT again, then the CBT will not be available for that VM.


  • Enable CBT for the VM using the below steps if the CBT value is disabled:
  1. Power off the VM
  2. Right click the VM, click "Edit settings", find the "Options" tab and click "Configuration Parameters"
  3. Set the "ctkEnabled" value to “False”
  4. Set the "scsi0:x.ctkEnabled" value to “False” for each disk of the VM in question
  5. Open the source folder and remove any -CTK.VMDK files
  6. Power on the VM
  7. Power off the VM again. This step is needed to update the CTK table
  8. Power on the VM
  9. Rerun Backup job
  • If the backup job is configured with single VM, then it is recommended to run the additional full backup.
  • If the backup job configured with multiple VMs and all the VMs in the configuration are facing the same issue, only then it is recommended to run an additional full backup.


  • It is not recommended to run an additional full backup if the backup job is configured with multiple VMs, and only part of the VMs are facing the above issue. You can run incremental backup for this scenario

  • It is not recommended to use a third-party application with the same VM configured for backup when you are using Vembu

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