Veeam: The specified network resource or device is no longer available

I had a problem with Veeam in combination with Hyper-V cluster and an Equallogic SAN. All backups would run fine using storage snapshots , except for one of them. Veeam would run the job but one of the VHDs for the vm could not be backed up and Veeam would fail with the shady error:

18/11/2013 17:00:24 :: Processing ‘VM’ Error: Client error: The specified network resource or device is no longer available. Failed to read data from the file [\\?\Volume{f0c726da-445d-11e3-8b10-91d33815ae43}\VM.vhd].
Failed to read data from the file [\\?\Volume{f0c726da-445d-11e3-8b10-91d33815ae43}\VM.vhd].”Exception from server: The specified network resource or device is no longer available.

Now when looking at the Event log of the Hyper-V host which hosts the VM I would see these errors regarding VSS with IDs: 12329 &13230  during the job:

This is the 12329 error:

Volume Shadow Copy Warning: A plug-and-play devnode could not be found for the volume while attempting to restart or remove the associated device.  The function GetHiddenVolumeDevinfo failed with 0×0000000000000002. The operation will be continue, however some state associated with this volume may not be cleaned up.

And then for the 12330:

Volume Shadow Copy Warning: The hardware shadow-copy volume \\?\Volume{f0c725f5-445d-11e3-8b10-91d33815ae43} disappeared unexpectedly. Check for any event logs reported by Plug And Play, by the hardware provider, or by volsnap

This last one gives us a clue about what’s going. I got a feeling that the Equallogic was in it since it talks about HW Snapshots disappearing. And sure enough:

Here we can see that the snapshot reserved space is insufficient for the backup to run a storage snapshot. The Equallogic deletes it because of it’s policy and that’s why Windows complains it disappeared unexpectedly.

Conclusion:

You need to either extend the snapshot reserve on the san or run backup without storage snapshotting.