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Change Block Tracking (CBT) and VM Backups in VMware




As I started my IT career from Backup Engineer to whatever today I am, I thought my first post on VMware should be on VM backup strategy, especially on Change Block Track for CBT mechanism  

CBT (Change Block Track) is allows backup applications to take incremental backups rapidly on VM. CBT uses VMware Storage API formerly known as VMware Storage API for Data Protection (VADP for more info https://kb.vmware.com/s/article/1021175). Below are the steps involved in enabling CBT on a VM.

       1).We need to define the CBT setting by configuring the VM configuration parameters ctkEnable= “True” (Advanced /General> Configuration Parameters).

       2).Above setting enables CBT global leve mean every disk can be tracked by CBT means you are allowed do a snapshot on VMDK file to track the changes for backup but independent or multi writer disks does not t like this setting to be enabled and it is not recommended too.

       3).We can ensure that required disk is only allowed to track by CBT by setting the parameter against to the SCSCIX.X.X disk.CTK setting to false or true for every disk attached on that particular VM.

With above setting backup applications now interact with VM Kernel to do a snapshot and track the changes from last backup, this feature not only helps the backup and it is used for vMmotion or VM storage motion.

I did not come across many issues w.r.t CBT except as mentioned above point no 2.
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