Changed block tracking and Guest defrag?

[rickardnobel]

If I understand it correctly the Vmware Data Recovery uses changed block tracking to spot the differences inside the VMs for each backup.

How does this work together with guest operating system defrag tools? If there is a defragmentation job running each night, would that not "change" a lot of blocks by just moving them around?

[jsykora · Accepted solution]

If for some reason you choose to defrag the VM using guest OS tools you will indeed change huge amounts of blocks. If you use the change block tracking to perform differential or incremental backups, they will be large.

Generally when your VMs sit on VMFS it's recommended not to defrag the guest OS.

[AndreTheGiant]

As written, a lot of blocks will changes...

And if you have a thin disk, you will see this disk become more larger after the defrag!

Andre

[cebomholt]

Agree with others- typically not recommended to defrag a guest OS. It will inflate your thin disks- and I believe that storage vMotion will help fragmentation of the vmdk.

[rickardnobel]

Thanks for your replies.