Microsoft VSS Troubleshooting

Last Updated: Aug 08, 2016 11:58AM PDT

Microsoft's Volume Shadow Copy is probably amongst the most complex functions of the Windows operating system; hence, if it breaks it's a time consuming process to repair.

Symptoms of a Volume Shadow Copy Malfunction

1. Very long (or seemingly indefinite) VSS snapshot generation time with intensive hard drive activity.
2. VSS errors reported in the Event Viewer (click start and search Event Viewer in search box to open)
3. VSS errors reported by Microsoft's Volume Shadow Copy tool vssadmin
4. VSS fails to create snapshots.

VSS Repair Strategy #1

1. Check your free disk space on ALL volumes/partitions on the PC where NovaBACKUP is installed. If disk space is too low VSS will cause the backups to fail if "Open File Backup" is enabled, which it is by default in NovaBACKUP.  VSS utilizes disk space on your partitions, not just the C: drive, to cache data.  VSS alone can utilize the remaining disk space on your partition and you would not even know it unless you knew about the command line functions to check that disk space usage for VSS.

2. Reboot. For some reason, servers that haven't been rebooted in a while cause VSS to malfunction. As all Microsoft veterans know, you need to reboot regularly as a preventive and cleanup measure for your system.

VSS Repair Strategy #2

You can try to re-register all VSS and COM components by following our FAQ on VSS Command Line Troubleshooting

VSS Repair Strategy #3

Uninstall all backup software on your computer, including Windows Backup if it's installed. You don't need to uninstall NovaBACKUP because NovaBACKUP doesn't contain or install any VSS writers; however, we have seen VSS writers of other backup software manufacturers cause system instability and errors.

After all other backup tools have been uninstalled, open the Registry Editor (regedit) as administrator and check the following branch: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\VSS\Providers

Underneath that key you should only find Microsoft Software Shadow Copy Provider 1.0 and no other VSS writer. If you do find another, it may be a residue registry entry of a previous backup software installation. You can save the entry by exporting the entire registry to a file (right click and select Export) and then it's safe to delete the entire branch entry underneath HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\VSS\Provider.

Then reboot and try again running vssadmin list writers to confirm the problem has been resolved.

VSS Repair Strategy #4

On some systems, the command vssadmin delete shadows isn't available. In Windows XP that's okay because VSS snapshots can't be persistent on XP (a reboot will get rid off them); however, on Vista you need to delete old shadows using:

vssadmin Resize ShadowStorage /For=C: /On=C: /MaxSize=300MB

300MB is usually the smallest amount you can specify and will effectively delete any existing VSS snapshots on your system.

If you don't get any VSS writer errors when using vssadmin list writers but the system isn't able to create a new VSS snapshot (and you have deleted all existing snapshots), then you may have to actually increase the max shadow storage size on your system. Use the previous command with a greater number, such as 10GB:

vssadmin Resize ShadowStorage /For=C: /On=C: /MaxSize=10GB

Note that it is also possible to allocate shadow copy storage space on a different drive, as along as it's local:

vssadmin Resize ShadowStorage /For=C: /On=X: /MaxSize=200GB

VSS Repair Strategy #5

Open vssadmin from the command line (run cmd as administrator).

Enter vssadmin delete shadows /all to clean up any dead VSS snapshots. Some defect systems accumulate hundreds of VSS snapshots that persist in the system and cause Windows to become unresponsive.

Enter vssadmin list writers and check for errors. If you receive any errors for one VSS writer, you may need to fix that particular VSS writer. It is common to receive writer errors caused by Microsoft's Virtual Server 2005 VSS writer.

If you see a VSS writer error, try the following:

Restart the services:

  • COM System Application Service
  • Distributed Transaction Coordinator Service
  • Volume Shadow Copy Service

and also restart the affected VSS writer service, for example Virtual Server 2005 VSS writer or Hyper-V VSS writer.

Check the Event Viewer for any additional error information logged by that VSS writer.

Run again vssadmin list writers to check if the above resolved the problem. If it didn't follow with the next strategy below:

VSS Repair Strategy #6

If the PC or server you are using is a virtual machine host, you need to install the latest VMware Tools (for VMware), Virtual Machine Additions (Virtual Server), on each virtual machine.

VSS Repair Strategy #7

Your computer may have a corrupt COM subscription information. Open the registry editor (regedit) and navigate to:


Then delete the Subscriptions key and reboot the machine.

A subsequent call in the command prompt should show no more errors: vssadmin list writers

This VSS repair strategy appears to work well when the System Writer is reporting an error. The Event Viewer may be reporting this or a similar error:

Writer Class Id: {e8132975-6f93-4464-a53e-1050253ae220}
Writer Name: System Writer
Writer Instance ID: {34162f4c-59ff-468e-848d-cb4b3d8dd7dc}

VSS Repair Strategy #8

Install the latest Service Packs and Updates through Windows Update.

Check Microsoft's Support for hot fixes and other updates to repair VSS.

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