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VADP backs up vSphere VMs from a central backup server or VM without backup agents, and does not require backup processing to be done inside each guest VM on the ESX host. This offloads backup processing from ESX hosts and allows each ESX host to run more VMs.
Changed Block Tracking (CBT) is a VADP feature that allows the VMkernel to track blocks that have changed. When an incremental backup needs to be performed, the blocks that need to be backed up can be quickly identified by the VMkernel, which improves incremental backup and replication times.