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How is changed block tracking (CBT) used in a vSphere implementation?
A. CBT is used by the VMkernel to reduce time needed for virtual machine copy operations.
B. CBT is used by VMware Data Protection (VDP) to reduce time needed for backup jobs.
C. CBT is used by vCenter Server to reduce the size of snapshots.
D. CBT is used by vSphere Replication for synchronous replication operations.
Correct Answer: B
Explanation/Reference:
Explanation:
Changed Block Tracking (CBT) is a VMware feature that helps perform incremental backups. Incremental backups reduce the backup time by only backing up the data that has changed since the last backup.
Virtual machines running on ESX/ESXi hosts can track disk sectors that have changed. This feature is called Changed Block Tracking (CBT). On many file systems, CBT identifies the disk sectors altered between two change set IDs. On VMFS partitions, CBT can also identify all the disk sectors that are in use.
Virtual disk block changes are tracked from outside virtual machines, in the virtualization layer. When software performs a backup, it can request transmission of only the blocks that changed since the last backup, or the blocks in use. The CBT feature can be accessed by third-party applications as part of the vSphere APIs for Data Protection (VADP). Applications call VADP to request that the VMkernel return blocks of data that have changed on a virtual disk since the last backup snapshot.
Incorrect Answers:
A: CBT is not used by the VMkernel to reduce time needed for virtual machine copy operations. Therefore, this answer is incorrect.
C: CBT is not used by vCenter Server to reduce the size of snapshots. Therefore, this answer is incorrect.
D: CBT is not used by vSphere Replication for synchronous replication operations. Therefore, this answer is incorrect.
References:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1020128