How to fix Error 5159 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 5159

Why This Error Happens

Error 5159 occurs when the SQL Server service account lacks the necessary file system permissions to read, write, or create a database file (MDF, NDF, or LDF) at the specified path. This can also result from the underlying disk or volume being offline, disconnected, or experiencing a hardware-level I/O failure. Additionally, antivirus software or Windows file locking mechanisms may be intercepting the operating system call before SQL Server can complete the operation.

Step-by-Step Resolution Guide

Step 1: Verify File and Folder Permissions

  • Navigate to the folder containing the database file (commonly C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\).
  • Right-click the folder, select Properties > Security, and confirm the SQL Server service account (e.g., NT Service\MSSQLSERVER) has Full Control.
  • If missing, click Edit, add the service account, and grant Full Control permissions, then click Apply.

Step 2: Confirm the Disk Volume Is Online and Healthy

  • Open Disk Management (diskmgmt.msc) on Windows Server 2025 / Windows 11.
  • Check that the volume hosting the database file shows a status of Online and Healthy.
  • If the disk shows Offline or Unknown, right-click the disk and select Online, then run chkdsk C: /f from an elevated Command Prompt to repair file system errors.

Step 3: Exclude SQL Server Directories from Antivirus Scanning

  • Open Windows Security or your third-party antivirus console.
  • Add exclusions for the SQL Server data, log, and backup directories (e.g., C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\*.mdf, *.ldf, *.ndf).
  • Restart the SQL Server (MSSQLSERVER) service via services.msc to apply the changes.

Step 4: Check for File Locks or Orphaned Handles

  • Use Process Explorer (Sysinternals) to search for any process holding a lock on the affected .mdf or .ldf file.
  • Terminate any non-SQL process holding the handle, or reboot the server if the lock cannot be released safely.
  • Attempt to bring the database back online using ALTER DATABASE [YourDB] SET ONLINE; in SQL Server Management Studio (SSMS).

Step 5: Validate SQL Server Service Account Configuration

  • Open SQL Server Configuration Manager, select SQL Server Services, and confirm the correct service account is configured under the Log On tab.
  • If the account was recently changed (e.g., from Local System to a domain account), ensure it has been re-granted NTFS permissions on the data/log directories as described in Step 1.
  • Restart the SQL Server service for changes to take effect.

Alternative or Verification Steps

  • Run sqlcmd -S localhost -Q "DBCC CHECKDB('YourDatabase')" to confirm the database is accessible and free of corruption after applying the fix.
  • If the issue persists, restore the affected database file from the most recent backup to a healthy volume and reattach it using CREATE DATABASE [YourDB] ON (FILENAME = 'NewPath\YourDB.mdf') FOR ATTACH;.