Unable to backup Live Virtual Machines in Server 2008 R2 Hyper-V


Symptoms


When backing up online Virtual Machines (VMs) using Windows Server Backup or Data Protection Manager 2007 SP1, the backup of the individual Virtual Machine may fail with the following error in the hyperv_vmms Event Log:

Log Name:      Microsoft-Windows-Hyper-V-VMMS-Admin
Source:        Microsoft-Windows-Hyper-V-VMMS
Date:          10/1/2009 12:52:19 PM
Event ID:      10137
Task Category: None
Level:         Error
Keywords:     
User:          SYSTEM
Computer:      Computername
Description:
No snapshots to revert were found for virtual machine 'VMName'. (Virtual machine ID 1CA5637E-6922-44F7-B17A-B8772D87B4CF)

Note: The Virtual machine ID will be specific to your Hyper-V installation and corresponding virtual machine.

Cause


During an online backup Volume Shadow Copy Service (VSS) requires mounting the snapshotted VHDs in order to revert them back to their proper state.  If automount is disabled, VSS cannot mount the snapshotted VHDs as required.

To determine if automount is enabled run DISKPART.EXE from a command prompt, and then run the following command without quotes at the DISKPART prompt:

 "automount"

Resolution


Enable the Automount feature using one of the methods below or use method 4 to fix the issue.

Method 1

Run DISKPART.EXE from a command prompt, and then enter the following command without quotes at the diskpart prompt:

 "automount enable"
 
Method 2

Use the following MOUNTVOL command without quotes:

 "mountvol /e"


Method 3

Edit the NoAutoMount registry value to enable automount.  If the value does not exist, add it.

Important: This method contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows


To resolve this issue, modify the registry. To do this, follow these steps:

1.  Click Start, click Run, type regedit in the Open box, and then click OK. 
2.  Locate the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MountMgr\

3.  Click Edit, point to New, and then click DWORD Value . 
4.  In the New Value #1 box, type NoAutoMount, and then press ENTER. 
5.  Right-click NoAutoMount and then click Modify. 
6.  In the Value data box, type 0, click Decimal, and then click OK. This will enable automatic mounting
7.  Exit Registry Editor. 

Method 4
 
1. Use SAN policy settings to avoid auto-mounting of new volumes (this could be done by setting the SAN policy to offline All)
2. Install the hotfix KB (2521348).

More Information