How to fix Error 5110 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 5110 – Network Path Not Supported for System Database Files

Why This Error Happens

This error occurs when SQL Server attempts to locate or create system database files (master, model, msdb, or tempdb) on a UNC network path (e.g., \\ServerName\Share) rather than a local drive letter path. SQL Server Database Engine requires direct, low-latency access to system database files for startup integrity and does not support UNC paths for these files, even if the account running SQL Server has full permissions to that share. This typically happens after a misconfigured installation, a startup parameter pointing to a mapped network drive, or an attempt to move system databases to a SAN/NAS location using an unsupported path format.

Step-by-Step Resolution Guide

Step 1: Identify the Current System Database File Locations

  • Open SQL Server Configuration Manager and check the SQL Server service Startup Parameters (tab in Properties) for -d, -l, and -e flags.
  • Look for any path beginning with \\ (UNC) instead of a drive letter like C:\ or D:\.
  • Alternatively, check the registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQLServer\Parameters.

Step 2: Move System Database Files to a Local or Supported Path

  • Stop the SQL Server service via Configuration Manager or net stop MSSQLSERVER.
  • Physically copy the master.mdf, mastlog.ldf, and other system database files from the network share to a local drive or a supported block-level SAN LUN (e.g., D:\SQLData\).
  • Ensure the destination folder has correct NTFS permissions granted to the SQL Server service account (Full Control).

Step 3: Update Startup Parameters to Reflect the New Local Path

  • In SQL Server Configuration Manager, edit the -d (master data file), -l (master log file), and -e (error log) startup parameters to point to the new local path.
  • Example: -dD:\SQLData\master.mdf, -lD:\SQLLogs\mastlog.ldf.
  • Save changes and close the Properties dialog.

Step 4: Restart the SQL Server Service

  • Start the SQL Server service again via Configuration Manager or net start MSSQLSERVER.
  • Monitor the SQL Server Error Log (ERRORLOG file) located in the MSSQL\Log folder to confirm the service starts without Error 5110.

Step 5: Reconfigure Any Dependent Jobs or Mapped Drives

  • If tempdb or other databases were also pointed to network paths via ALTER DATABASE ... MODIFY FILE, update those paths using T-SQL to a local or supported storage path.
  • Restart the instance again after applying file path changes for tempdb, since tempdb is rebuilt at every startup.

Alternative or Verification Steps

  • Verify the fix by checking the SQL Server Error Log for a clean startup message: “SQL Server is now ready for client connections” with no Error 5110 entries.
  • If local disk space is a constraint and network storage is required, use an iSCSI or Fibre Channel SAN configuration that presents the storage as a local drive letter (block-level access) rather than a UNC/SMB file share, since SQL Server fully supports block-based network storage but not file-share (UNC) paths for system databases.