Windows Event ID 326 – Volsnap: Volume Shadow Copy Service Writer Error

Start by examining the VSS writer status and gathering detailed event information to identify the failing component.

1. Open Event Viewer → Windows Logs → System and locate Event ID 326 entries
2. Note the timestamp and any additional error codes in the event description
3. Run the following PowerShell command to check VSS writer status:

   vssadmin list writers

4. Look for writers showing "Failed" or "Unknown" state in the output
5. Use PowerShell to get detailed VSS information:

   Get-WmiObject -Class Win32_ShadowCopy | Select-Object DeviceObject, InstallDate, VolumeName

6. Check the Application log for corresponding writer-specific errors:

   Get-WinEvent -FilterHashtable @{LogName='Application'; Level=2} -MaxEvents 50 | Where-Object {$_.TimeCreated -gt (Get-Date).AddHours(-2)}

Restart the VSS service and re-register all VSS writers to resolve temporary communication issues.

1. Open an elevated Command Prompt or PowerShell session
2. Stop the Volume Shadow Copy service:

   Stop-Service -Name VSS -Force

3. Wait 30 seconds, then restart the service:

   Start-Service -Name VSS

4. Re-register all VSS writers using the following commands:

   cd /d %windir%\system32
   vssadmin register provider
   for /f "tokens=*" %i in ('dir /b *.dll') do regsvr32 /s "%i"

5. Specifically re-register core VSS components:

   regsvr32 /s ole32.dll
   regsvr32 /s oleaut32.dll
   regsvr32 /s vss_ps.dll

6. Verify writer registration status:

   vssadmin list writers | findstr "Writer name\|State"

7. Test VSS functionality by creating a manual shadow copy:

   vssadmin create shadow /for=C:

Analyze system resources and storage subsystem health to identify performance bottlenecks affecting VSS operations.

1. Check available disk space on all volumes, especially the system volume:

   Get-WmiObject -Class Win32_LogicalDisk | Select-Object DeviceID, @{Name="Size(GB)";Expression={[math]::Round($_.Size/1GB,2)}}, @{Name="FreeSpace(GB)";Expression={[math]::Round($_.FreeSpace/1GB,2)}}

2. Monitor memory usage during backup operations:

   Get-Counter "\Memory\Available MBytes", "\Memory\Pages/sec" -SampleInterval 5 -MaxSamples 12

3. Check for disk errors using CHKDSK:

   chkdsk C: /f /r /x

4. Examine VSS storage area allocation:

   vssadmin list shadowstorage

5. Increase VSS storage area if needed:

   vssadmin resize shadowstorage /for=C: /on=C: /maxsize=20%

6. Review Windows Performance Toolkit logs for I/O bottlenecks:

   Get-Counter "\PhysicalDisk(_Total)\Avg. Disk Queue Length" -SampleInterval 1 -MaxSamples 60

Modify VSS writer timeout values to accommodate slower systems or applications that require extended processing time.

1. Open Registry Editor and navigate to:

   HKLM\SYSTEM\CurrentControlSet\Services\VSS\Settings

2. Create or modify the following DWORD values to increase timeout periods:
   • MaxDiffAreaFileSize = 3221225472 (3GB in bytes)
   • MinDiffAreaFileSize = 314572800 (300MB in bytes)
3. Navigate to the VSS writer-specific timeout settings:

   HKLM\SYSTEM\CurrentControlSet\Control\BackupRestore\FilesNotToSnapshot

4. Use PowerShell to configure VSS timeouts programmatically:

   $regPath = "HKLM:\SYSTEM\CurrentControlSet\Services\VSS\Settings"
   Set-ItemProperty -Path $regPath -Name "MaxDiffAreaFileSize" -Value 3221225472 -Type DWord
   Set-ItemProperty -Path $regPath -Name "MinDiffAreaFileSize" -Value 314572800 -Type DWord

5. Restart the VSS service to apply changes:

   Restart-Service -Name VSS -Force

6. Test the configuration with a manual backup operation
7. Monitor Event Viewer for Event ID 326 recurrence

Enable detailed VSS tracing to capture comprehensive diagnostic information for complex writer failures.

1. Enable VSS debug logging by modifying the registry:

   $vssRegPath = "HKLM:\SYSTEM\CurrentControlSet\Services\VSS\Debug"
   New-Item -Path $vssRegPath -Force
   Set-ItemProperty -Path $vssRegPath -Name "Trace" -Value 1 -Type DWord
   Set-ItemProperty -Path $vssRegPath -Name "TraceLevel" -Value 0xFFFFFFFF -Type DWord

2. Configure trace file location:

   Set-ItemProperty -Path $vssRegPath -Name "TraceFile" -Value "C:\VSS_Trace.log" -Type String

3. Restart VSS service to enable tracing:

   Restart-Service -Name VSS

4. Reproduce the backup failure that triggers Event ID 326
5. Analyze the trace file for detailed error information:

   Get-Content "C:\VSS_Trace.log" | Select-String -Pattern "Error|Failed|Timeout"

6. Use Windows Performance Toolkit for advanced analysis:

   wpa.exe C:\VSS_Trace.etl

7. Disable tracing after troubleshooting to prevent performance impact:

   Set-ItemProperty -Path $vssRegPath -Name "Trace" -Value 0 -Type DWord

8. Collect additional diagnostic information using built-in tools:

   vssadmin list providers
   vssadmin list volumes
   wmic shadowcopy list brief