Instructions for CBT resetting
During backups of virtual machines the VMware API's may have problems collecting the change block tracking information of a specific virtual machine. When this occurs the entire VMDK will be backed up, not just the used space. When this occurs it may be necessary to reset the Change Block Tracking for the virtual machine.
Steps to reset CBT
Note: Before doing these steps verify that the virtual machine does not have any current snapshots and the virtual machine is Hardware Version 7 or higher.
1. Power off the VM.
2. Right click on the VM, select Edit Settings. Select the Options tab, select the General setting and click the box for Configuration Parameters
3. Change the ctkEnabled value to false
4. 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)
Note: There may be multiple listings for this entry if the virtual machine has multiple VMDK files. All entries should be set to false.
5. Open the folder the virtual machine is stored in on the datastore and remove any -CTK.VMDK files
6. Power on the VM.
7. 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.
8. Power on again the VM.
9. 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)