Unable to mount one or more Hyper-V guest VHDs from the backup

Error code

Product

Applies to

BA4921

BackupAssist

For BackupAssist v8 or later.

Description

The backup verification was unable to test-mount a guest VHD in the backup.

Resolution

The VHD mounting errors are explained in the Backup Verification section of the backup report. The explanation of each error will include a description of the cause. Resolve the errors and perform a manual test restore to confirm the integrity of the backup.

When troubleshooting problems with Hyper-V backups, it is important to first determine which guest/s is causing the error. You can do this by checking the Hyper-V VMSS logs, as shown below. You may also be able to identify the guest from the information in the backup report. If you are not able to identify the guest, try backing up the guests one at a time until the errant guest is found.

The guest causing the error can be confirmed by running the backup again without that guest and checking that the backup runs without errors. You can also try a VSS backup on the guest itself using a trial version of BackupAssist. The success or failure of this backup will help to further narrow down what could be causing the error.

If the problem is with backing up data within a guest, will you need to open the Event Viewer inside that guest and review the VSS log entries. These may identify the exact cause of the VSS error.

  1. Click the Start button.
  2. Click Control Panel.
  3. Click System and Maintenance.
  4. Click Administrative Tools.
  5. Double-click Event Viewer.
  6. In the left hand navigation window, browse to Applications and Services Logs > Microsoft > Windows > Hyper-V-VMMS.

Last updated

Created

Further assistance

8th January 2018

06th May 2014

BackupAssist Support page