Error Code [91:9] Volume Shadow Copy Service (VSS) error. VSS service or writers may be in a bad state.

Backup operation fails with Volume Shadow Copy Service (VSS) error.

Symptoms

Backup operations are failing with the following error message:

Volume Shadow Copy Service (VSS) error occurred on host [HOSTNAME]. VSS service or writers may be in a bad state. Please check vsbkp.log and Windows Event Viewer for VSS related messages, or run "vssadmin list writers" from a command prompt to check the state of the VSS writers; if the "Microsoft Hyper-V VSS Writer" reports an error, please restart the "Virtual Machine Management Service (vmms.exe)"

Causes

The error message appears due to one of the following reasons:

Cause 1:

The Volume Shadow Copy creation of one or more Virtual Machines (VM) have failed. This prevents the VMs from being backed up.

Cause 2:

VSS Writer was in an unstable state before the backup job started. This symptom can be verified by checking the status of the writer by running the command: \"vssadmin list writers\". If the VSS Writer is missing from the list, or is listed as in an unstable state, this causes backups of Hyper-V virtual machines to fail.

Cause 3:

When automatic mounting of new volumes on Windows 2008 Hyper-V host system is disabled, the online backups of (capable) guest systems will fail. Automatic fallback to an offline guest backup is not attempted.

Cause 4:

VSS Writer fails when the default path to the cluster shared volume does not match the Hyper-V Manager's path to the cluster shared volume. Mismatched paths are recorded in the following entries in the vsbkp.log:

3048 1318 08/09 09:59:23 126 CsSnapRequestor::AddVolumesToSnapshotSet() - CvClusterPrepareSharedVolumeForBackup successful for vol:[C:\ClusterStorage\Volume1\] VolPathName:[C:\ClusterStorage\Volume1\]

3048 1318 08/09 10:00:25 126 CsSnapRequestor::AddVolumesToSnapshotSet() - Call m_vss->AddToSnapshotSet(vol, m_shadowProvider.GetProvider(), &id) [FAILED, throwing CV exception] - Code = 0x80042306, Description = VSS_E_PROVIDER_VETO

Cuase 5:

Windows Application Event viewer displays the following VSS error message:

Volume Shadow Copy Service error: A critical component required by the Volume Shadow Copy service is not registered.

If an error occurred during Windows setup or during installation of a Shadow Copy provider, a recent installation of a third-party hardware provider may contribute to this failure, .

Cause 6:

A volume inside one of the VMs may have run out of space, thereby preventing the Volume Shadow Copy creation.

Cause 7:

If one of the backed up VMs has information about a virtual hard disk that no longer exists on the drive, then the backup operation may fail.

Resolution

Solution 1:

Identify the VM that is causing the backup failure by looking at the application, system, and Hyper-V VM events in Windows Event Viewer.

Solution 2:

Restart Hyper-V Virtual Machine Management Service to bring back the VSS writer to a stable state, which is necessary for backups. If this writer goes into an unstable state frequently, analyze the root cause from the Windows Event Viewer.

Solution 3:

Enable automatic mounting. To change the Mount Manager setting for the automount of new volumes, run one of the following commands:

• Using the DISKPART command-line options

• Using the Mountvol command

• Using the REGISTRY Key

• HKLM\SYSTEM\CurrentControlSet\Services\MountMgr\NoAutoMount 0 - enables automatic mounting

References

http://technet.microsoft.com/en-us/library/dd252619(WS.10).aspx

http://technet.microsoft.com/en-us/library/cc753703(WS.10).aspx

Solution 4:

From the Hyper-V Manager console, rename the path to the VHD. For example, if the path to the VHD file is: ""file:///C://ClusterStorage//volume1/">C:\ClusterStorage\volume1",

Rename it to  ""file:///C://ClusterStorage//Volume1/">C:\ClusterStorage\Volume1" to match the case. Note that the only difference is the case of the letter 'V'.

Solution 5:

1. Identify and temporarily uninstall any third-party VSS Hardware provider (Example: NetApp SnapDrive).
2. If the backup succeeds, re-install the software.

Solution 6:

1. Make sure that the volumes in the Guest operating systems have a minimum of 500 MB free space.
2. Run the backup operation again.

Solution 7:

1. Identify the virtual hard disk that no longer exists, and remove its information from the Virtual Machine settings
2. Run the backup operation again.