Unable To Release Guest. Error: VSSControl: Failed To Freeze Guest, Wait Timeout

I installed Veeam Backup and Replication 6 for VMware. It was backing up my virtual machines fine, but I got the following error on some SQL servers:

Unable to release guest. Error: VSSControl: Failed to freeze guest, wait timeout Error: VSSControl: Failed to freeze guest, wait timeout

It’s pretty easy to understand what the error is, but not obvious how to fix it. The error is basically saying that there’s a problem with VSS on the guest VM. In my case the guest VM was a Microsoft SQL Server (2008 R2, but this works for all SQL versions: MSSQL 2008, SQL 2005, SQL 2000, SQL 2012, etc…).

First thing to do is run the following command in the command prompt:

vssadmin list writers

This will tell you if there’s an error with the VSS writer. You’ll probably notice that there’s a timeout on the SQL VSS writer, hence the Failed to freeze guest, wait timeout part of the error.

To fix this, you need to restart the SQL VSS Writer service. If you are getting the error because of some other VSS issue, it might help to restart on of these other services:

  • swprv
  • vss
  • ReportServer
  • winmgmt
  • EventSystem
  • vmvss (If you’re backup is of a VMware VM)
  • VMTools (If you’re backup is of a VMware VM)
  • VMUpgradeHelper (If you’re backup is of a VMware VM)

The following is a useful table of VSS writers and the Windows service that they correspond to. For example, if the ASR Writer is failing, you need to restart the Volume Shadow Copy service.

VSS Writer

Service Name

Service Display Name

ASR Writer VSS Volume Shadow Copy
BITS Writer BITS Background   Intelligent Transfer Service
COM+ REGDB Writer VSS Volume Shadow Copy
IIS Config Writer AppHostSvc Application Host   Helper Service
IIS Metabase   Writer IISADMIN IIS Admin Service
Microsoft Exchange   Writer MSExchangeIS Microsoft Exchange   Information Store
Microsoft Hyper-V   VSS Writer vmms Hyper-V Virtual   Machine Management
Registry Writer VSS Volume Shadow Copy
Shadow Copy   Optimization Writer VSS Volume Shadow Copy
System Writer CryptSvc Cryptographic   Services
WMI Writer Winmgmt Windows Management   Instrumentation

If you are using Veeam Backup and Replication and vssadmin isn’t showing errors when listing the VSS writers, you may need to increase the wait timeout. The default is 15 minutes, but you can increase this in Veeam with the following registry change:

For 32bit operating systems: In HKEY_LOCAL_MACHINE\SOFTWARE\VeeaM\Veeam Backup and Replication

For x64 operating systems: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Veeam\Veeam Backup and Replication

Add a DWORD value named VssPreparationTimeout

The value is in milliseconds (decimal), increase this number to something higher than the millisecond equivalent of 15 minutes then restart the services.

Veeam recommend half an hour for some systems.

Also a reboot of the server you are trying to backup can fix this :)

And in case this SQL holds VC database, you have to add the host directly: http://www.veeam.com/KB1051

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2 thoughts on “Unable To Release Guest. Error: VSSControl: Failed To Freeze Guest, Wait Timeout

  1. Thanks a lot.
    This information was very useful for us !!!

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    • Hey José,

      Glad you found the Veeam Backup and Replication information useful, that Unable to release guest error can be a pain and diagnosing VSS issues with backups is never fun.

      If you have time, please subscribe to my blog. I have only sent out 1 subscription email since setting up the option to subscribe earlier this year, but when I do it’s really useful stuff.

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