The backup fails with a Microsoft VSS Error, "A problem with Windows Shadow Copy was detected":
As the error suggests, if you take a look at the Hyper-V VMMS event log (Event Viewer → Application and Services Logs → Microsoft → Windows → Hyper-V-VMMS → Admin), you'll find the following event:
Source: Hyper-V VMMS | Event ID: 10112
The number of volumes reverted does not match the number of volumes in the snapshot set for virtual machine 'Exchange' (Virtual machine ID 3C942666-F9E0-45C4-A376-716B7BDCA877).
This error is caused whenever the number of volumes reverted does not match the amount of volumes found in the shadow copy taken. This could be due to numerous reasons explained further hereunder.
- Ensure that you do not have storage pools inside the VM since they would cause such an error, since they're not supported.
- Ensure that you do not have encrypted disks within the virtual machine.
- Ensure that there isn't another application using VSS inside the VM. Such as Windows Backup, replication jobs or any other backup/replication job.
- Ensure there is a minimum of 10% free space on each of the drives inside the VM for Microsoft VSS to complete successfully.
- Please try to update the Integration services on this particular VM and then reboot it and re-test the backup. This can be checked by connecting to the virtual machine and then go to 'Action' > 'Insert Integration Services Setup Disk'.
- Check if the VM has any snapshots/checkpoints, if so merge them. Also check for any pending merges. If so ensure that you shut down the VM to allow the merge to complete successfully.
- Check if there are any offline disks in the Disk Management of both VM and host. If so, bring these disks online or dismount them and try again.
- Check the Windows 'System' event log for any partmgr 58 events:
Warning partmgr 58
The disk signature of disk 2 is equal to the disk signature of disk 0.
This would indicate a conflict in Disk ID's between the host and VM, which would cause such an error. Instructions to change the Disk ID can be found here.