Good post by Luca Dell’Oca (thank you)
Lately, different bugs involving VMware CBT in vSphere 6 have created some justified concerns among users. But there are ways to guarantee successful backups even in these conditions.
Image-level backups are still the way to go
Yes, vSphere 6 is having some issues with CBT in vSphere 6.
Since its introduction back in the days of vSphere 4.0, CBT has been the cornerstone to allow fast incremental backups. CBT (change block tracking), as the name says, is a log of changed blocks of a virtual machine that vSphere registers in a file. Different data protection solutions can read this file, list which blocks have been changed since a given timestamp (usually the previous job execution), and thanks to this easily retrieve only those blocks from the storage instead of having to do a full backup every day.
Read on here