VSS Troubleshooting Guide – Failed VSS Writers (4034380)

AppAssure/Rapid Recovery is using Volume Shadow Copy Service (VSS) as part of the recovery point creation process. If the VSS subsystem isn’t functioning properly, then product will not be able to complete the backups. The following sections are designed to help remedy specific VSS issues that may occur within your system.

Note: Additional VSS troubleshooting details can be found in Microsoft TechNet articles and various other online resources. These documents provide additional troubleshooting steps that go beyond the scope of this article.

You may run into failed backups for machines with the following errors:

Windows Registry Disclaimer:

Quest does not provide support for problems that arise from improper modification of the registry. The Windows registry contains information critical to your computer and applications. Make sure you back up the registry before modifying it. For more information on the Windows Registry Editor and how to back up and restore it, refer to Microsoft Article ID 256986 “Description of the Microsoft Windows registry” at Microsoft Support.

1. Reboot your agent server: Servers that have not been rebooted in a while may cause VSS to malfunction. You should reboot your server regularly as a preventive and cleanup measure for your system.
2. Reset the writers to a stable state:
   • In an elevated Command Prompt, type
     vssadmin list writers , Enter.
   • If any writer is noted as failed or has an error, or any writers’ states are not listed as stable, reset the writers by running vshadow.
   • In an elevated Command Prompt change directory to the location of vshadow.exe. Vshadow can be found at:
     • For Replay4: C:\Program Files (x86)\AppAssure Software\Replay Agent\Utils6
     • For AppAssure/Rapid Recovery: C:\Program Files\apprecovery\agent
   • Type vshadow , Enter (e.g. vshadow C: or vshadow C: D: E:)
   • List the writers again to check their stability: type vssadmin list writers , Enter.
   • If any writers remain in a failed state or have an error, please continue to the next step.
3. Clear existing shadows: VSS has a limit on the number of snapshots that can be kept on the system; these snapshots take up space on the drive that is needed to take these snapshots. The following steps will clear this space.
   • In an elevated Command Prompt, type vssadmin delete shadows /all , Enter.
     • If you have receive the following error: "Error: Snapshots were found, but they were outside of your allowed context. Try removing them with the backup application which created them."
     • Return to the elevated Command Prompt, type wmic , Enter.
     • Type shadowcopy delete , Enter.
     • For each shadow copy it lists, type Y , Enter. When all shadow copies have been deleted type exit , Enter.
     • In some cases DISKSHADOW will need to be used to delete the existing shadow copy. For more information please read KB 121604 .
   • Return to the elevated Command Prompt, type vssadmin list writers , Enter.
   • If any writers remain in a failed state or have an error, please continue to the next step.
4. Restart the services:
   • Open Services.msc and restart the following services:
     • COM+ Event System
     • COM+ System Application Service. This may not be started (if not, start it)
     • Distributed Transaction Coordinator Service
     • Volume Shadow Copy Service
     • If possible, restart affected VSS writer services. For example, Virtual Server 2005 VSS writer or the Hyper-V VM manager Service to the Hyper-V VSS writer.
       For a little more details on the services associated with different writers, please read KB 129774
   • Check the Event Viewer for any additional error information logged by that VSS writer.
   • Return to the elevated Command Prompt, type vssadmin list writers , Enter.
   • If any writers remain in a failed state or have an error, please continue to the next step.
5. Shadow Storage Maximum Size: As noted above, VSS has a limit to the amount of space that it uses take and keep snapshots. Default values of 5% or 10% (depending on OS) per volume may not be large enough for large snapshots. Best practice is to set the Shadow Copy Storage Area to No limit.
   • Servers can resize storage using Disk Management or Command Line. Most desktop operating system can only use the Command Line.
   • Disk Management:
     • Open Disk Management, diskmgmt,msc, methods vary by OS
     • Right click on the first volume listed, select Properties, and select the Shadow Copies Tab.
     • Select the first Volume on the list
     • Click Settings, select No limit, and click OK. Repeat for all Volumes.
   • Command Line: In an elevated Command Prompt, type vssadmin  resize shadowstorage /for=/on=/maxsize=unbounded , Enter (e.g.  vssadmin resize shadowstorage /for=C: /on=C: /maxsize=unbounded)
6. If you do not receive 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), continue with the following steps:
   • Uninstall all backup software on your computer, including Windows Backup if it is installed. We have seen VSS writers of other backup software manufacturers cause system instability and errors.
   • In an elevated Command Prompt type regedit , Enter. Go to HKLM\SYSTEM\CurrentControlSet\services\VSS\Providers, expand the folder, and check listed providers
   • You should only find Microsoft Software Shadow Copy Provider. If you do find others, they may be residual registry entries from previous backup software installations. You can save the entry by exporting the residual providers folder (right click and select Export) and then it’s safe to delete the entire branch entry underneath.
   • Reboot, open an elevated Command Prompt, type vssadmin list writers, Enter to confirm the problem has been resolved.
7. If the Server or PC you are using is a virtual machine host, you need to install the latest VMware Tools (for VMware), Virtual Machine Additions (Virtual Server),or integration tools (Hyper-V) on each virtual machine.
8. If you have completed all the above noted steps and you are still getting either VSS errors or unable to complete a snapshot, we recommend that you contact Microsoft Technical Support, as the issue is related to a malfunction within VSS or the Windows operating system.