Backing up Virtual Machines in ESXi 6.0.x with Changed Block Tracking enabled returns incorrect changed sectors

SUMMARY

VMware has announced a bug related to ESXi 6.0.x whereby backing up a changed block tracking enabled virtual machine in ESXi 6.0.x returns incorrect changed sectors.

ISSUE

The Issue:
Virtual machine backups utilizing Changed Block Tracking (CBT) in ESXi 6.0 may experience the following symptoms:

• The CBT API call QueryDiskChangedAreas() API call can sometimes return incorrect changed sectors, which results in inconsistent incremental virtual machine backups.
• Inconsistent virtual machine backups

Caution:
After applying the patch, a host reboot is required. In addition, you must reset CBT on your virtual machines (see: How to Reset Change Block Tracking (CBT) for VMware Backups) and run a full backup to ensure data is consistent going forward.

• Downgrade the affected ESXi hosts to version 5.5, and downgrade the virtual Hardware Version from 11 to 10, if necessary. For more information, see VMware Knowledge Base articles Reverting to a previous version of ESXi (1033604) and Downgrading the virtual machine hardware version in ESX/ESXi (1028019).
• Shutdown the virtual machine before doing an incremental backup.
• Do a full virtual machine backup rather than an incremental backup.
• Additionally, customers may utilize a Unitrends agent for backups within the VMs.

• If you are using Eager Zeroed thick virtual disks, just a full virtual machine backup is sufficient to resume incremental virtual machine backups.
• If you are using other types of virtual disks, a full reset of CBT data is required, see VMware KB 2139574, Resetting Changed Block Tracking for VMware vSphere virtual machines.