VSS Troubleshooting for BackupVault Pro
When backing up Windows machines to BackupVault, the 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.
1. 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
Warning: 21:48:35 Unable to open file: C:\Program Files\IT Support Computers\Diagnostics\ServiceHost_20100620192402.xml,
reason:\\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy191\Program Files\IT Support Computers\Diagnostics\Diagnostics\ServiceHost_20100620192402.xml (The system cannot find the file specified)
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.
2. VSS backups randomly fail if Sophos antivirus is installed
The Sophos endpoint agent writes to the Windows registry a certain way and often causes the MS Volume Shadow Copy Service (VSS) to time out. The backup then fails.
Follow these steps by Sophos to resolve the issue.
3. Failed At Freeze Errors
These are often caused by other third party software that uses VSS. See this Microsoft Failed At Freeze article for a workaround.
4. Warning: Failed to read security descriptor for file ... (Access is denied)
This warning is common when the BackupVault Pro service does not have access to the file to be backed up. Ensure the BackupVault Pro ESE service has read access to all the files you require to be backed up.