Problem Description
The SQL Server VSS Writer service fails to register and is consequently absent from the vssadmin list writers command output. This absence results in the failure of Volume Shadow Copy Service (VSS) based backups for SQL Server databases. Accompanying symptoms can include VSS errors in the Event Viewer or the service being stuck in a "starting" state or failing to start altogether.
Cause:
A frequent yet often overlooked reason for the SQL Server VSS Writer's malfunction is inadequate free disk space.
This issue can stem from low space on the volumes containing SQL Server database files or on the primary system drive.
The VSS framework and its writers, including SQLWRITER, demand a certain amount of available space to function correctly.
This space is essential for creating snapshots, storing metadata, and writing operational logs. When disk space becomes critically low, these processes fail, causing the writer to become unstable or unlisted.
Resolution:
To resolve this issue, ensure there is adequate free disk space on all relevant volumes:
Identify Affected Drives:
Check the drive(s) where your SQL Server data files (.mdf, .ndf) and log files (.ldf) are stored.
Check the system drive (usually C:), as this is where the operating system, VSS components, and temporary files reside.
Consider any dedicated VSS shadow copy storage volumes if configured.
Free Up Disk Space:
Delete Unnecessary Files: Remove old backups, temporary files, downloaded installers, or other non-essential data.
Empty Recycle Bin: Ensure the Recycle Bin is empty.
Clean Up Temporary Directories: Use Disk Cleanup utility (cleanmgr.exe) to remove system temporary files, log files, and more.
Move Data: If possible, move non-SQL Server related data to a different volume or archive.
Extend Volume (If feasible): If physical disk space allows, extend the logical volume using Disk Management.
Restart Services:
Once sufficient disk space has been reclaimed, restart the following services in order:
SQL Server VSS Writer
Volume Shadow Copy (if it was stopped or in an error state)
COM+ System Application (if restarting VSS did not help)
Verify the Writer:
Open an elevated Command Prompt and run:
vssadmin list writers
The "SQL Server VSS Writer" should now appear in the list with a "Stable" state.