VSS Troubleshooting

When backing up Windows machines to BackupVault, the Attix5 Pro client uses Microsoft Volume Shadowcopy Storage (VSS) to access specific applications and open files.

VSS uses “Copy On Write” to handle changes to files when they are open. This concept is explored in more detail in our how VSS works article.

Whilst VSS allows consistent application and open file backups, users can experience problems backing up which can be confusing. This article explains basic troubleshooting steps.

Vssadmin list writers

The command vssadmin list writers will display a list of all the vss writers installed on the machine, and any error conditions associated with them.

For a VSS writer to work it must be:

  • Shown when the vssadmin list writers command is run.
  • In a stable state.

If it is not shown or in an error state, there is almost certainly a VSS problem with the Windows host.

Check the event log for any VSS errors, and you may find a resolution by searching the Internet for any error codes shown.

If you are unable to find a resolution, you should contact Microsoft support who will be able to assist.

Insufficient Volume Shadowcopy Storage Area Disk Space.

As the understanding VSS FAQ explains, the amount of disk space required for a VSS backup varies depending on the amount of change during any backup.

One troubleshooting technique is to either remove the Storage Area limit, or relocate the disk space used to a different volume to allow for additional space, and therefore more changes to be tracked during a backup attempt.

Increasing the Volume Shadowcopy Storage Area will often allow backups to complete where they could not previously.

Errors encountered include:

  • Error: 10:04:12 Unable to read from file:D:\Data\MyDatabase.mdf, reason: There is not enough space on the disk
  • Error: 18:12:01 Unable to read from file:D:\Data\MyFile.dat, reason: Insufficient system resources exist to complete the requested service


To change the settings, open the Disk Properties then go to Shadow Copies and click on Settings

You can then click on No Limit to remove the limit, or use the Located on this volume pull down to change the volume where the shadow copy area is stored.

VSS Errors

When running a backup, you may encounter the following error:

Message: 10:05:06 Starting VSS snapshot
Error: 10:05:07 An error occurred trying to initialize VSS: Unknown VSS or COM error
Warning: 10:05:07 VSS could not be started and was disabled

VSS is CPU architecture dependent. If the incorrect backup client version is installed, VSS will not be able to function.  A common cause of this issue is having the Attix5 Pro 32-bit Backup Client installed on a 64-bit operating system.

Whilst the client installer MSI prevents installation to the incorrect architecture, you may encounter problems if the client has been installed manually or if using a legacy client installer.

A quick way to detect the problem is if using the default installation path, you notice "(x86)" in the installation file or working paths, indicating that 32-bit program files are being used, e.g.: C:\Program Files (x86)\Attix5 Pro\Backup Client SE\toBackup.

Another way to detect the problem is if you find that the VSS writers are not shown in the Backup Client when trying to back up MS Exchange or MS SQL using VSS, but the VSS writers are visible and stable when using “vssadmin list writers”.

To resolve the issue, uninstall the 32-bit Backup Client, install the 64-bit Backup Client and reconnect to the Backup Account. Make sure that you also reinstall any applicable plug-ins.

File Access Warnings

Unable to open file warnings

Warning: 21:48:35 Unable to open file: C:\Program Files\My Cloud\Diagnostics\ 20150620192402.log, 

reason:\\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy191\Program Files\My Cloud\Diagnostics\ 20150620192402.log (The system cannot find the file specified)

This error message is seen when a file is in use, and is therefore being handled by VSS (VSS creates the GLOBALROOT snapshot path).

VSS ages out the oldest data in the Volume Shadowcopy Storage Area when it runs out of space. When you encounter this error message, it often indicates that the snapshot of the file is no longer available as VSS has overwritten it due to insufficient space.

You may need to increase the Volume Shadow Copy Area as described above to resolve the problem.

The cause may also be another VSS error, so check the event logs for Volsnap or Volume shadow copy errors.


Warning: 21:47:05 Failed to read security descriptor for file: C:\Program Files\My Cloud\Diagnostics\ 20150620192402.log, reason: \\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy191\ Program Files\My Cloud\Diagnostics\ 20150620192402.log (Access is denied)

This error message is seen when a file is in use or an application file, and is being handled by VSS.

The error occurs when the Attix5 Pro service user does not have permission to access the original file, but is displayed as a VSS path here as the original file is in use and Attix5 Pro is trying to access the snapshot copy.

To resolve this error, ensure that the Attix5 Pro service user has read access to all files that you wish to back up. If you are backing up Exchange, SQL or Hyper-V, this also applies to the application files such as .edb, .mdf or VHD files.