VSS Troubleshooting for BackupVault Pro

Introduction

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. When Windows attempts to back up a disk volume, a Volume Shadow Copy Snapshot is created for the volume. When the snapshot is created, any Volume Shadow Copy Service (VSS) writer associated with the volume is called. If any of the VSS writers encounter an error, the entire backup job will fail. This article explains basic troubleshooting steps.

Command Line Troubleshooting

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.

Whilst vssadmin list writers is the most common tool for troubleshooting, it is not the only one. Below are the command options available in the vssadmin toolset.

• vssadmin list providers – Lists all registered VSS providers
• vssadmin list writers– Lists all subscribed VSS writers
• vssadmin create shadow– Creates a new shadow copy
• vssadmin delete shadows– Deletes shadow copies
• vssadmin list shadows– Lists existing volume shadow copies
• vssadmin list shadowstorage – Lists volume shadow copy storage associations
• vssadmin add shadowstorage – Adds a volume shadow copy storage association.
• vssadmin delete shadowstorage– Deletes volume shadow copy storage associations.
• vssadmin resize shadowstorage– Changes the maximum size of the shadow copy storage area or the volume in which the shadow copies are stored

Common Errors

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. Could not prepare for snapshot creation (VSS writer in an unexpected state):

• 0x800423f2; ‘failed at freeze’
  • These are often caused by other third party software that uses VSS. See this Microsoft Failed At Freeze article for a workaround.
• 0x800423f4; ‘failed at prepare snapshot'[‘Writer Name:…’]
  • When the snapshot is created, any Volume Shadow Copy Service (VSS) writer associated with the volume is called. If any of the VSS writers encounter an error, the entire backup job will fail. Check the writer name given in the error code and restart the writers associated service. If possible, reboot the machine.

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.

5. Backup failed to complete…

• Timed out waiting for VSS operation to complete:
  • This is due to high disk activity causing the VSS operation to fail. Reschedule your backup to run when disk activity is not so high.
• 0x8004230f; unexpected provider error:
  • This is caused by the backup initiating when another VSS provider is already running. From the backup client, open Options > Advanced > VSS > set the VSS provider to Microsoft Software Show Copy Provider.
• 0x80042313; flush writes timeout:
  • This is due to high disk activity causing the VSS operation to fail. Reschedule your backup to run when disk activity is not so high.
• 0x8004232c; nested volume limit:
  • This is usually seen on VM hosts when the volume it is attempting to backup is available on the host as well as the VM so there is a logic failure between the host VSS writers and VM VSS writers. Check all the drive volumes on the host machine and make sure none are mapped drives / VHD assigned to VMs. The specified volume is nested too deeply to participate in the VSS operation. Possible reasons for this error include the following:
    • Trying to create a shadow copy of a volume that resides on a VHD that is contained in another VHD.
    • Trying to create a shadow copy of a VHD volume when the volume that contains the VHD is also in the same shadow copy set.

6. Error: The SQL Server VSS Writer is offline

This error can be caused by a number of misconfigurations. Check this SQL troubleshooting guide for more information.

VSS writer and services

Every VSS writer has an associated service which is responsible for starting it. Below is a list of all writers and their services. Use this guide when determining which services to restart in the event of a writer failure.