CBT Reset Failure

Product version: 9.1

Last modified: 01 October 2019


The error message states 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 uses the VMware CBT technology to identify which data has changed since the last job run. Several factors – such as a power outage – can cause VMware CBT to reset and lose track of the incremental changes for a VM.The error message appears when the CBT error handling is set to reset CBT and automatic CBT reset fails. For more information on CBT, see VMware KB 1020128.


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

  1. Check the .vmx file of the VM and make sure that the following options are present:

    • ctkEnabled = "TRUE"

    • scsi0:0.ctkEnabled = "TRUE"

If the VM has multiple disks, this option must be present for each disk.

  1. Check the VM folder on the datastore. Make sure that there is a -CTK.VMDK file for each disk.

If any of the above conditions are not met, reset CBT as follows:

  1. Power off the VM.

  2. Right-click the VM and choose Edit settings.

  3. Open the VM Options > Advanced > Configuration Parameters.

  4. Click Edit Configuration.

  5. Set the ctkEnabled value to false.

  6. Set the scsi0:x.ctkEnabled value to false for each disk.

  7. Open the VM folder on the datastore and remove any -CTK.VMDK files.

  8. Power on the VM.

  9. Power off the VM again. This step is required to update the CTK table.

  10. Power on the VM.

  11. Run the backup or replication job.