Discussions specific to the Microsoft Hyper-V hypervisor
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Full Name: AP_

Re: The infamous 'VSS_WS_FAILED_AT_PREPARE_SNAPSHOT' problem

Post by ap_ » Jun 15, 2018 8:00 am

Bennon Maina wrote:
Another way around this, although wouldn't recommend it on backups jobs for VMs with high I/O that are failing to create at preparing a snapshot/checkpoint; create one manually from Hyper-V Manager or SCVMM.
Once completed, delete the snapshot. All AVHDX files associated with the VMs will be merged but do check the storage location in case any are left. You should be able to delete them manually and run a backup job.

I haven't had a backup failure since.
Thanks for this information Bennon, very much appreciated! I couldn't find any orphaned AVHDX files (perhaps I was looking in the wrong place) but your solution of creating and deleting a checkpoint (followed by a restart) on the guest vm has fixed my issue.

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Full Name: Michael Tribe

Re: The infamous 'VSS_WS_FAILED_AT_PREPARE_SNAPSHOT' problem..

Post by migmjt » Mar 01, 2019 11:32 am

Case ID 03391638.
I had this problem on one VM and turned off integration services for a while. I then tried turning them back on after some successful backups but it failed again. I turned integration services off again and it started backing up again. Then another VM stopped backing up recently. I raised a case with Veeam and got a lot of advice about VSS being in stable state, restarting services, updating integration services, updating Veeam itself etc etc. Nothing helped.

I then tried making checkpoints in Hyper-V for both VMs and they started backing up again. I removed the checkpoints and they failed again.

In the end I had a look in the VM folders on the cluster storage and noticed there were some 5 month old Autorecovery.avhdx files sitting there. I removed all checkpoints and then renamed the avhdx files as .old. I did this with the VMs running to be sure they weren't required - I figured they'd be locked if they were in use so was fairly confident they were obsolete when I could rename them. (I deleted them once I was sure I didn't need them). The backups started working fine again.

I watched the backup process and saw that Veeam creates these files briefly for each VM then they disappear. I guess something went wrong one time and they got left behind (both VMs had the same timestamp on these files). Having the old files must get in the way of Veeam making new ones I suppose.

So if you get the 'VSS_WS_FAILED_AT_PREPARE_SNAPSHOT' problem when backing up with Veeam in Hyper-V, have a look in the VMs folders on you Hyper-V host / cluster storage and check you don't have any rogue checkpoint files. If you do try moving them out of the folder or renaming them and try a backup.

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Full Name: Derek

Re: The infamous 'VSS_WS_FAILED_AT_PREPARE_SNAPSHOT' problem..

Post by dsapergia » Apr 02, 2019 3:30 pm

The cause of my encountering this issue was the fact that one of my Virtual Machine's VHDX files was in the root of its Cluster shared volume and not in a folder. ie c:\ClusterSharedVolumes\server1\serverdisk2.vhdx moving it to c:\clusterSharedVolumes\server1\vhdx\serverdisk2.vhdx resolved the issue. For some reason MS Servers can't properly work with these files in the root of CSV volumes, we first encountered the issue with Virtual Machine Manager.

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