ESXi's been borking VM backup and there's no fix yet

Sounds familiar - there was a similar "feature" with "large" VMs and CBT a while back. VMware's getting careless?

Cbt

Says it all really, they have you by the short and dangleys and relying on server 2012 backup to vhdx is not much better.

More Bugs

in vSphere these days than a Motel in Sudan

fixed today, download the vmware patch

fixed today, download the vmware patch

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2137546

Summaries and Symptoms

This patch updates the esx-base VIB to resolve an issue that occurs when you run virtual machine backups which utilize Changed Block Tracking (CBT) in ESXi 6.0, the CBT API call QueryDiskChangedAreas() might return incorrect changed sectors that results in inconsistent incremental virtual machine backups. The issue occurs as the CBT fails to track changed blocks on the VMs having I/O during snapshot consolidation.

Patch Download and Installation

The typical way to apply patches to ESXi hosts is through the VMware vSphere Update Manager. For details, see the Installing and Administering VMware vSphere Update Manager.

ESXi hosts can be updated by manually downloading the patch ZIP file from the VMware download page and installing the VIB by using the esxcli software vib command. Additionally, the system can be updated using the image profile and the esxcli software profile command. For details, see the vSphere Command-Line Interface Concepts and Examples and the vSphere Upgrade Guide.

Reset-CBT powershell cmdlet

The patch is available but you have to Reset CBT on all enabled VMs, after applying the patch.

Have a look at this powershell script that help you automate this operation in multiple VMs.

http://blogs.unitrends.com/vmware-cbt-reset-powershell-cmdlet/