How to reset Change Block Tracking (CBT) for VMware Backups

Problem

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 (CBT) for the virtual machine.

At the time of writing this article VMware themselves had acknowledged that a CBT reset may be required if issues are seen during backup operations in VMware KB 1020128 (https://kb.vmware.com/s/article/1020128)

Error Message

From the beremote debug log:

[fsys\vmvcb]         - SymVmTools: GetDiskChangedInfoAPI: SYM_VMC_ERROR:  SOAP_ERROR
[fsys\vmvcb]         - SymVmTools: SOAP 1.1 fault: "":ServerFaultCode [no subcode]
"Error caused by file /vmfs/volumes/DATASTORE/VIRTUAL MACHINE/VIRTUAL DISK.vmdk"
Detail: <FileFaultFault xmlns="urn:vim25" xsi:type="FileFault"><file>/vmfs/volumes/DATASTORE/VIRTUAL MACHINE/VIRTUAL DISK.vmdk</file></FileFaultFault>

Solution

To reset the CBT:
1)  Disable the CBT by following the steps documented by VMware KB 1020128 https://kb.vmware.com/s/article/1020128 (make sure you are following the disable CBT steps)

To disable CBT, ensure that there are no existing snapshots for the virtual machine.

2) Use Backup Exec to run a full backup after disabling CBT.
 

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