Sign in
Get Help

Serious VMware vSphere 6 Changed Block Tracking Bug


Describes a serious CBT bug in vSphere 6.0 environments.



Release 8.1 for Recovery-Series and Unitrends Backup appliances and software will support hypervisor-level backups for vSphere 6.
At the time of this KB, internal testing with vSphere 6.0 has exposed a bug in the changed block tracking (CBT) code of the hypervisor that can cause data corruption and unrecoverable backups. VMware has confirmed the issue, and has released KB 2114076.

Note: This can affect anyone doing hypervisor-level backups with vSphere 6.0.

We continue to work with VMware on the issue and will update once VMware has released a fix.
As a result, we recommend that you do NOT upgrade to vSphere 6.0 if you are doing hypervisor-level backups using VMware. If you are using vSphere 6.0, we recommend leveraging guest protection at the file- and application-level to ensure those VMs are protected efficiently until VMware provides a fix for the CBT issue.


VMware has issued a patch and they have acknowledged that the issue has been resolved. This is the pertaining KB -

Have more questions?

Contact us

Was this article helpful?
0 out of 0 found this helpful

Provide feedback for the Documentation team!

Browse this section