Changed Block Tracking (CBT)

Changed Block Tracking (CBT) is an incremental backup technology for VMware virtual machines (VMs). 

Like snapshot differentials or delta differencing,  CBT backs up only the blocks that have changed, rather than backing up every block of every VM in the infrastructure. CBT requires ESX/ESXi hosts at version 4.0 or newer, VMs at virtual hardware version 7 or newer, and that I/O operations go through the ESX/ESXi storage stack. 

CBT is disabled by default; 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. 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.

VMware acknowledges that CBT could lose track of incremental changes in the event of a power failure or hard shutdown.

See also: vSphere Replication

Contributor(s): Meredith Courtemanche
This was last updated in March 2013
Posted by: Margaret Rouse

More News and Tutorials

There are Comments. Add yours.

TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

Research More Tech Terms

  • Search thousands of tech definitions
  • Browse tech definitions
    Browse Alphabetically:

Powered by

File Extensions and File Formats

File Extension and File Formats List:

Powered by