A bug published on 30th July 2019 has been found in VMware Change Block Tracking (CBT) that can corrupt backup data.  



TL;DR - Reverting a snapshot will cause VMware CBT to report incorrect data to your backup solution, resulting in corrupted and possibly unrestorable backups


The official KB article from VMware shows that this is by design, however if you are using any backup product for your VMware hosts then you should take precautionary steps immediately to avoid your backup data being corrupted.


Recommended actions:


  1. Every time you revert a VM snapshot in VMware, you must reset CBT data for that VM.
    Further Instructions can be found in the below KB article:
    How to reset CBT of a VMware VM - https://help.altaro.com/support/solutions/articles/43000493306

  2. To ensure the above action is taken on every reverted snapshot, you should also Create a VMware alarm to be triggered on every Snapshot revert action that completes, this will remind your admin to reset CBT data for the VM.

    The trigger event for this alarm should be:
    The virtual machine state has been reverted to a snapshot 


  3. If a backup was taken with incorrect CBT data returned, it is necessary to take a fresh backup set for that VM as this would have caused a corrupted backup set.