vss writers keep failing

Use vssadmin list writers immediately after a backup failure to see which writers are failing and what error codes they report. Different error patterns point to different root causes.

1. Check for timeout and resource issues

• If vssadmin list writers shows writers in a Failed state with retryable or timeout-related errors (for example, 0x800423f4, 0x800423f3, 0x800423f2, or VSS_E_WRITERERROR_TIMEOUT / VSS_E_WRITERERROR_OUTOFRESOURCES), reduce system load during backup:
  • Ensure there is sufficient free disk space on all volumes involved in the backup and on the shadow copy storage area.
  • Avoid running other heavy I/O tasks (AV scans, large file copies, defrags, etc.) during backup.
  • On systems with slow disks, low memory, or low CPU, consider scheduling backups at off-peak times.
• Review the Application and System event logs for VSS- and VolSnap-related errors (for example, VolSnap Event ID 25 indicating that the diff area file could not grow in time). This indicates high I/O or misconfigured diff area causing shadow copies to be aborted.

2. Restart affected writers and hosting services

• After a failure, run vssadmin list writers and identify which writers are Failed.
• For writers hosted in the VSS service (registry writer, COM+ class registration database writer, shadow copy optimization writer, ASR writer), restart the Volume Shadow Copy service.
• For writers hosted by applications (SQL, Exchange, NTDS, DHCP, WINS, etc.), restart the corresponding application/service.
• If writers show VSS_E_WRITERERROR_RETRYABLE, retrying after restarting the hosting service is appropriate. If they continue to fail repeatedly, investigate that specific application’s logs and configuration.

3. Fix the case where no writers are listed (if seen) If at any point vssadmin list writers returns no writers at all and the Application log shows VSS errors such as:

• VSS Event ID 34: “The VSS event class is not registered.”
• VSS Event ID 8193 with CoCreateInstance errors

Then repair the VSSEvent registration:

1. Open regedit.
2. Go to: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\EventSystem\{26c409cc-ae86-11d1-b616-00805fc79216}\EventClasses\{FAF53CC4-BD73-4E36-83F1-2B23F46E513E}-{00000000-0000-0000-0000-000000000000}-{00000000-0000-0000-0000-000000000000}
3. Ensure the TypeLib value exists and its type is REG_EXPAND_SZ and its data is: %systemroot%\system32\EVENTCLS.DLL
   • If the type is wrong, delete the value and recreate it as an Expandable String Value named TypeLib, then set the data as above.
4. Restart the COM+ Event System and Volume Shadow Copy services.
5. Run vssadmin list writers again and confirm writers are listed.
6. Consider hotfixes and configuration review

• Repeated, random writer timeouts on Windows Server under high I/O can be caused by known VSS writer timeout issues. Review event logs for timeout-related VSS errors and apply any relevant hotfixes or updates that address VSS writer timeouts.
• Also verify:
  • Disk write cache and storage performance (especially on domain controllers or heavily loaded servers).
  • That audit logs or other logs are not excessively large, which can contribute to timeouts.

If, after reducing load, correcting registry configuration (if needed), and restarting the relevant services, the same writers still fail repeatedly, focus on those specific writers (for example, SQL, NTDS, Exchange) and their own logs/configuration, as the failure may be within the application rather than VSS itself.

References:

• No VSS writers are listed when you run vssadmin list writers
• No VSS writers are listed when you run the vssadmin list writers command in Windows Server
• Time-out errors occur in Volume Shadow Copy service writers, and shadow copies are lost during backup and during times when there are high levels of input/output
• Writer Errors and Vetoes