How to Fix VSS_WS_FAILED_AT_POST_SNAPSHOT and Prevent It
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In our test lab we regularly encounter a somewhat typical Volume Shadow Copy Service Error (VSS) error reported in the backup service or application may be:
Details: Writer 'Microsoft Hyper-V VSS Writer' is failed at 'VSS_WS_FAILED_AT_POST_SNAPSHOT'. The writer experienced a transient error. If the backup process is retried, the error may not reoccur.
The above VSS error message tells you which VSS writer is at fault and may also be reported by other writers, including:
‘ASR Writer’
‘BITS Writer’
‘COM+ REGDB Writer’
‘IIS Config Writer’
‘IIS Metabase Writer’
‘Microsoft Hyper-V VSS Writer’
‘MSSearch Service Writer’
‘Performance Counters Writer’
‘Registry Writer’
‘Shadow Copy Optimization Writer’
‘SqlServerWriter’
‘System Writer’
‘Task Scheduler Writer’
‘VSS Metadata Store Writer’
‘WMI Writer’
Steps to Fix this Error:
Once you know which writer is affected you need to dig deeper into the logs of that particular writer.
The quick way: If you have .Net Framework 4 installed (Server 2012 and later has it pre-installed) you can use the tool VssDiag on BackupChain‘s website to get all necessary info from the Windows logs.
The usual, manual way: As always, the Windows Event Viewer is your best friend. Check the Application and System log at the time when the backup application reported the error +/- 10 minutes.
If the error is caused by Hyper-V VSS Writer:
In addition to the above, and most importantly in the case of Hyper-V, check Applications and Services Logs -> Microsoft -> Windows -> Hyper-V-Config
and Hyper-V-VMMS, Hyper-V-Worker, Hyper-V-Hypervisor and all other Hyper-V logs in there.
Most likely there is a clue in there if the error has something to do with Hyper-V.
If the error is not caused by Hyper-V, check the logs of the related, VSS aware service, such as Microsoft Exchange or SQL Server.
From our experience, the cause of the error is 99% somewhere logged in the Event Viewer. Unfortunately the information may be spread around and it may take time to find all pieces. But hey, being an IT admin rocks, doesn’t it? Check this article for an “ego boost” 😉