What is change block tracking in Vsphere?


We can see in some of the backup software there is an option available called change block tracking and use change block tracking for improving the backup performance (backup, restore & replication).

CBT is a new feature in vSphere that can keep track of the blocks of a virtual disk that have changed since a certain point in time. This is extremely useful for backup and replication applications that can use this information to greatly improve incremental backup and replication times.

This feature can be enabled or accessed through 3rd party applications (like any backup software) as a part of the Vstorage API for data protection.

Applications can use the API to query the VMkernel to return the blocks of data that have changed on a virtual disk since the last backup operation. You can use CBT on any type of virtual disk, thick or thin and on any datastore type except for physical mode Raw Device Mappings. This includes both NFS and iSCSI datastores.

The prerequisite of CBT is that the VM must use the version min 7 or later.

The CBT feature is disabled by default; the reason for this is there is a very small bit of overhead that occurs when using it. However this overhead is a small price to pay for the great efficiencies that happen by enabling it. This feature is not global and can be enabled on only select VMs that you want to take advantage of this functionality. It can be enabled either through the vSphere client or by using the SDK.

More info: http://itknowledgeexchange.techtarget.com/virtualization-pro/what-is-changed-block-tracking-in-vsphere/

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