Changed Block Tracking, is a feature of vSphere (Driver is within the VMkernel). CBT identifies changed blocks within a VM’s disk, and logs these in a tracking file.
vRanger can utilize VMware's CBT feature to reduce the time needed for backups and replications, by only utilizing the blocks that have changed. This will often result in reduced resource consumption for network and storage elements.
CBT is not enabled by default. Please note, that utilizing CBT does impose minimal overhead on the associated ESX(i) host.
To Enable CBT using vRanger: