A. I'm a big Microsoft fan, but it's a pretty well known fact that sometimes the corporation makes decisions that don't make sense.

Hyper-V provides a great VSS writer that lets VSS snapshot requests be forwarded to guest OSs so that the integrity of virtual machine (VM) backups is ensured as the VSS writers in the guest OSs are activated.

Windows Server has a backup application, Windows Server Backup. Many companies may use the in-box backup application to back up their Hyper-V servers, thinking the great Hyper-V VSS writer is being used. Well, it's not. By default, the VSS writer for Hyper-V isn't registered with Windows Server Backup, which means the backups you make with the in-box tool aren't calling the VSS writers in your VMs. The backups you make of your virtual hard disks may not actually be usable in a restore situation.

The solution is to register the VSS writer with Windows Server Backup manually.

  1. Start the registry editor (regedit.exe) on the Hyper-V box.
  2. Navigate to HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion.
  3. From the Edit menu, select New then Key and enter a name of WindowsServerBackup. Select this new key.
  4. Under WindowsServerBackup, create a new key called Application Support.
  5. Under Application Support, create a new key called \{66841CD4-6DED-4F4B-8F17-FD23F8DDC3DE\}, as shown below.
  6. Under this key, create a String value (Edit New then String Value) named Application Identifier and press Enter.
  7. Double click the new value and set the value data to Hyper-V. Click OK.
  8. Exit the registry editor.

Click to expand.

Alternatively, save the following into a file named hypervvsswriterregister.reg then double-click it.

Windows Registry Editor Version 5.00

\[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT
\CurrentVersion\WindowsServerBackup\Application
 Support\\{66841CD4-6DED-4F4B-8F17-FD23F8DDC3DE\}\]
"Application Identifier"="Hyper-V"

This will create the keys and values for you.

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