Resizing VHDX and VBR Replication/Backup

[tomtom94]

Hello!

I need to expand a VHDX file of a Hyper-V VM.
This VM and a few others are being backed up at night and replicated at daytime to another host with VBR. (with 6 checkpoints)
I searched and found a few information snippets but no best practices.

From the perspective of VBR:
What is the best way to do it?
Is it better to expand the VHDX while the vm is running or in offline mode?
Backup job:
Do i need to make an active full backup no matter how i expand the VHDX?

Replication job:
Do i need to delete the complete replication data of that VM or can i merge all replication checkpoints, then expand the merged/replicated VHDX and continue the replication job?

Best regards,
Thomas

[david.domask]

Hi Thomas,

Active full should not be required as far as I know, but as a "safety precaution" it's not a bad idea. However I believe that RCT will not work for the next run if I remember right so it will do a full READ of the disk, but it should be incremental after processing the data and knowing what is knew. I did the changes while the production machine was running and there were no issues and I'm not aware of specific best practices on this, but I would imagine with the machine powered off it's "safest".

For the replication job, I tested quick in my lab and just expanded/shrank/compacted the source VM a few times, and replica job continued on without issues, though it did have a substantially higher READ after the changes likely because of the disk resizing.

[tomtom94]

Hello David!

Thank you for your reply and testing.
I was a bit uncertain because my search brought up following Veeam KB but its rather old and i guess no longer valid for newer VBR Versions: https://www.veeam.com/kb2450
Then i read an article stating that RCT cant track changes while the VM is shutdown so it would be better to resize the VHDX while the VM is running.
And in the helpcenter https://helpcenter.veeam.com/docs/backu ... ml?ver=120 i found the following statement: --> "[For VMs with VHDX disks] If you change the size of VM disks on the source VM, Veeam Backup & Replication resets changed block tracking (CBT)."
And that would explain the read intensive actions you did notice.

I think i will do it like you tested:
- pause/disable replication job
- incremental backup (just in case)
- online resizing VHDX
- unpause/enable replication job
- active full backup at night
- and finally after all old checkpoints are merged into the replicated VHDX i will mount it read only to check if it has the new size

Best regards,
Thomas

[david.domask]

Aha, I think your plan is solid, and I can understand the uncertainty. Indeed that KB is a bit old, but the part about Expanding should still be valid. And yes, at worst, I think the most you'd get is just that RCT isn't used for one incremental run (large read, but not write), and then the backups will behave as usual.

[tomtom94]

Hello!

Sorry i totally forgot to post the results of the resizing ...

I did an online resizing of the VHDX and next replication job took longer but worked without a problem. (sadly couldnt check system resources because i got a call from another customer)
Like expected the replicated VHDX still had the old size but after all the old checkpoints were migrated the file showed all the changes.

Best regards

Thomas

[david.domask]

Hi Thomas,

Thanks for sharing the results and glad it all turned out okay