incremental backup from time-shifted VBR

[alesovodvojce]

This is rather a question on how stuff works, than a problem. This happened:

Code: Select all

Sunday, incremental backup is made
Monday, incremental backup is made 
Tuesday, we needed to return back the snapshot of VBR guest OS to Sunday (snapshot reverts everything - system AND backup storage)

Now
On Tuesday, incremental backup is made. Increment between Sunday and Tuesday. But the backed-up guests know that they have been backed-up on Monday and (presumably) tracking changed blocks since.
How can they pass throught VSS writer the correct data about difference between Sunday and Tuesday, while the last snapshot was on Monday?

Yes they passed the correct data, at least SureBackup is able to run from them:)

[Andreas Neufert]

OK ... I think we mixed here some things.

Change Block Tracking (VMware CBT, Veeam CBT for Hyper-V and RCT for Hyper-V) work pretty the same way. Whenever there is a new SnapShot all new changes of a VM are marked with one number higher.
In your case
Sa Snapshot number 100
Monday SnapShot number 101
Tuesday SnapShot number 102

So if you reverted VBR and Backup-Data back to state 100 it will back up everything that is higher. That way many backup programs can work with same change block tracking informations as well.

The only problematic situation can be if you look at Logfile and Archive Log Backup as it will be deleted over time. So you loose some granlular backup possibillities of timeframe from Sunday to Tuesday as the lgfiles were delted by your old job.

[alesovodvojce]

Thanks a lot for explanation how stuff works. Now I feel confident that what I saw was not just a random thing but something we can rely upon.