What happens when you backup a VM outside the normal job?

[cparker4486]

Hello,

Does backing up a VM outside its regular job impact what's backed up in the regular job?

Asked another way, is CBT calculated per VM between runs of the same job or each time a VM is backed up by a job?

[Andreas Neufert]

Any CBT works that way that it will increment the internal state flag for changed blocks by 1 when you create a new snapshot. It doesn´t matter if VM snapshot was done manually or by different backup vendors.

What a Veeam job knows is that the latest backed up state number was let´s say 23. If someone now started other backup jobs or created manual snapshots, the new state number is maybe 29. But Veeam still knows it needs to backup every block labeled with number above 23 at the next incremental run.

[cparker4486]

Oh I see. I was under the impression that CBT was a flag of true/false and that it was reset when a backup was taken.

Instead, you're saying that each backup of a VM, for the same job, is a diff between the old and new state of that VM. CBT facilitates a fast method to perform that diff (as opposed to the slow method of a block-by-block comparison.)

Do I have it right?

[Andreas Neufert]

Correct we know the old state, look into CBT what has changed and read only those block areas. Multiple backups or 3rd party backups do not affect this.