question about backup size vs move drive to other VM

[lohelle]

I have a backup job with some VMs, including a current and a new file server.

If I move disk2 from the current file server to the new file server (detach - attach in vCenter), what will happen?
I guess all data will have to be read (no CBT), but can I expect that the backup size should not increase very much?

And what if I create a new big drive on the new file server, and then copy all the data in Explorer. If I detach the old storage-drive before the backup runs, can I expect that the data is already in the backup file, and that deduplication will save me from getting a big increase in backup file size?

[Vitaliy S.]

Hi Lars,

If I move disk2 from the current file server to the new file server (detach - attach in vCenter), what will happen? I guess all data will have to be read (no CBT), but can I expect that the backup size should not increase very much?

Yes, that's correct, there will be no CBT at the first job pass. As to the backup size, then can you please tell me what backup mode you use? Reversed or forward incremental? If you are using reversed incremental backup mode, then the VBK file will not increase much, since data is already there and will be deduped.

And what if I create a new big drive on the new file server, and then copy all the data in Explorer. If I detach the old storage-drive before the backup runs, can I expect that the data is already in the backup file, and that deduplication will save me from getting a big increase in backup file size

I'm not sure about that, since data blocks inside the Guest OS do not "correlate" with the blocks on the virtual disk level (depends on the fragmentation level on the previous disk and new one etc.). I would recommend just re-attaching the disk to the new server. It will be much quicker since you will not need to copy data using File Explorer first and then spend extra time backing up this disk.

Thanks!

[lohelle]

I ran the backup (incremental), and the result was somewhere in the middle of the "scenarios". We did the "new disk + copy"-approach. Approx 3/4 of the disk-size was sent to the remote repository, but the incremental was approx 1/5 of the total disk size.
The file server stores a mix of MS Office documents, jpg og pdf.

[Vitaliy S.]

Yes, data will be re-send in any case, it doesn't matter since the disk you attach is a new disk to the VM being backed up. I was just referring to target storage. With reversed incremental backup mode (assuming you've added new VM to the same job) you should have good savings ratio.