vss snapshot limit

[marieelieg]

Hi everyone,

I have a Hyper-V cluster with 19 hosts. I have 30 LUNs containing multiple VMs. Those LUNs are presented to the 19 hosts.
I created a backup job containing some VMs. 2 VMs failed with the following error: Unknown status of async operation.
I searched online and found this kb article: https://www.veeam.com/kb1846. This article said to increase the limit for the vss snapshot (15% - 20% of the volume).

My question is what volume? 20% of the C:\ drive of the hyper-v host? Or 20% of the LUN of the VM? Or ...?

Thank you guys in advance. Your help is much appreciated.

[Vitaliy S.]

Since VSS snapshot is created across all volumes, then you need to select all disks/volumes where VMs are located at. Also, if you have the same issue during application-aware processing operation (VSS task), then you should do it inside the guest OS which failed in the job.

On a side note, I would also send debug logs to our support team to make sure you're facing exactly this issue which is mentioned in the KB.

[alanbolte]

"Unknown status of async operation."
This is a generic error; the KB is about the event log entry "cannot find anymore diff area candidates for volume"

VSS troubleshooting can be complicated, and must primarily rely on Windows event logs rather than Veeam logs. Please contact Support.

[marieelieg]

Mmmm i will contact support.

But as to what Vitaly said: "select all disks/volumes where VMs are located". Every LUN is around 500GB to 1TB. So if I take all of them, lets say half of them 500GB and the other half 1TB, that makes for the 30 LUNs = 22.5 TB. And 20% of that = 4.5TB. So that means I have to reserve 4.5 TB on the local host?? The C:\ drive is 250GB, I can't reserve 4.5TB on a 250GB volume.

I don't know if what I just said is right but that's how I understood it. Any more elaboration on this matter is very much appreciated.

[nmdange]

The vss snapshot is stored as part of the volume where the snapshot is taken (in the "System Volume Information" folder), it's not stored on the C drive.

Edit: Looking at that KB article, the instructions aren't really correct, you'd need to right-click the CSV you want to modify, not the C drive. Though I don't think that would fix the error you're getting.

[marieelieg]

Okay but there is a "System Volume Information" folder on every partition on my computer and my computer has only the C:\ drive. So the snapshot should be created on the C:\ drive. Right? In that case how do I do my calculations?

[Vitaliy S.]

VSS snapshot is created on each volume, not on the drive C. On a side note, once you open a support case, please update this topic with a case ID for future readers. Thanks!

[marieelieg]

In that case how do I change the limit of the shadow copies on each LUN? because if I right click each LUN, I don't get "Configure Shadow Copies..." in order to adjust the limit.

[Vitaliy S.]

Our support team should assist you with this task after verifying that you're experiencing the VSS space related issue.

[marieelieg]

Okay thank you everyone. Tomorrow I will open a case and post the case number here:D

[alanbolte]

Hi marieelieg, I'm actually working on improving that KB at the moment, so I'd like some input on how to make it less confusing.

Clearly the first step is to reword the Challenge section so that it's clear from the first line what issue the article is about, instead of needing to carefully read the whole paragraph.

It doesn't matter how you get to the Shadow Copies menu, so maybe I should replace 'a' with 'any'? Or maybe it would be better to just say to run C:\Windows\System32\VSSUIRUN.exe as administrator...
One point that definitely needs clarification is that you need to click on the particular volume before clicking 'settings'. All of the volumes should be in that list, regardless of whether they are set up as drive letters, mount points, or aren't mounted at all.

I'll also add instructions for configuring the limits from command line. Anything I'm missing?

[marieelieg]

All of the above are great. Just one more thing. There is a line in the Solution paragraph that says: "Typically 15-20% of the volume is needed to create shadow copies". If you could specify 15-20% of what volume to take in our calculations.
Thank you in advance.

[marieelieg]

Case number: 01965674 as promised

[alanbolte]

I think I might see the confusion. Your LUNs are likely presented as C:\ClusterStorage\Volume#; you should be able to select these paths separately from C: in the Shadow Copies utility.

[marieelieg]

Hi alanbolte,

That's exactly how the LUNs are presented. In Veeam, when I right click a Hyper-V host > Manage Volumes, I can see the C: drive and the LUN paths (C:\ClusterStorage\Volume#) seperately. I can change the concurrent VSS snapshots for them, etc.
However in windows, when I right click a volume > Configure Shadow Copies..., I only get the C: drive to change its settings.

That's why I'm asking 15-20% of which volume should I take in my calculations. Only the C: drive? or all the LUNs which is not logical because 20% of all LUNs = 4.5TB and the C: drive is only 250GB (the only drive that appears in the "Configure Shadow Copies..." window, that I can change the VSS limit for).

If you can help me with this I would really appreciate it.
Thank you in advance

[alanbolte]

I do not know why your mount points would not be listed in the shadow copy utility on the Hyper-V host. Can they be altered using the commandline utility 'vssadmin resize shadowstorage'?

If you are unable to make progress with our support, you may need to request the case be escalated, and/or open a case with Microsoft.