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ID: KB0030
Product Version: 5.6
Last Modified: 28 Apr 2015


A job fails with an error message stating that VMware CBT cannot be reset for a VM and suggests resetting CBT manually.


After the initial full VM backup or replication, all consequent job runs are forever incremental. By default, NAKIVO Backup & Replication relies on VMware CBT technology to quickly identify what data has changed since the last job run. If an ESXi host is unable to provide a correct CBT data for a VM, the product behaves according to the CBT error handling settings specified in step 4 of VM backup jobs and VM replication jobs. By default, the product tries resetting VMware CBT, so it can be used on consequent job runs. If the product's request to reset VMware CBT fails, the above error message appears.


Check whether VMware CBT settings are properly configured for the VM:

  1. Check .vmx file of the VM and make sure following options are present:
    ctkEnabled = "TRUE"
    scsi0:0.ctkEnabled = "TRUE" (if the VM has multiple disks then you should have this option for each disk)
  2. Check the VM folder on the datastore and make sure that there is the-ctk.vmdk file for each disk of the VM.

If any of the above conditions is not met, try resetting CBT by following the steps below:

  1. Power off the VM.
  2. Right click the VM, click Edit settings, go to the Options tab, click General, and then 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.
  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. Run the backup or replication job to re-enable CBT.
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