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.
Explanation:
B is correct
Administrators can enable CBT and some backup tools enable it automatically. If any blocks were changed since the last backup, Changed Block Tracking tags them and stores the information in a CTK file in the Virtual Machine folder by default. CBT tells the vSphere or third-party backup tool to copy these changed blocks, avoiding copies of the entire VM. This reduces the amount of data undergoing backup.
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1020128
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Changed Block Tracking (CBT) is a VMware feature that helps perform incremental backups. VMware Data Recovery uses this technology and so can developers of backup and recovery software.
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http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2078744
日本語ページ
変更ブロックのトラッキング（CBT）は、差分バックアップの実行に役立つ VMware の機能です。VMware Data Recovery はこの技術を使用しています。また、バックアップおよび復旧ソフトウェアの開発者もこれを使用できます。
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