How to fix Error 5143 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 5143 – Concurrent Operation Failed on File

Why This Error Happens

Error 5143 occurs when SQL Server 2025 attempts a concurrent I/O operation (such as sparse file allocation, instant file initialization, or snapshot operations) on a database file, but the underlying Windows I/O subsystem rejects the request. This is typically caused by the SQL Server service account lacking proper NTFS permissions on the file/volume, antivirus or backup software locking the file during the operation, or the underlying storage (especially on ReFS/Storage Spaces Direct volumes) not supporting the specific sparse/concurrent I/O flag being used. In some cases, this is also triggered by disk corruption or a mismatch between the file system block size and SQL Server’s expected sector alignment.

Step-by-Step Resolution Guide

Step 1: Verify File and Folder Permissions

  • Open File Explorer and navigate to the SQL Server data directory (e.g., D:\SQLData\MSSQL16.MSSQLSERVER\MSSQL\DATA).
  • Right-click the .mdf/.ndf/.ldf file in question, go to Properties > Security, and confirm the SQL Server service account (e.g., NT Service\MSSQLSERVER) has Full Control.
  • Alternatively, run this PowerShell command to grant permissions:
  icacls "D:\SQLData\MSSQL16.MSSQLSERVER\MSSQL\DATA" /grant "NT SERVICE\MSSQLSERVER:(OI)(CI)F" /T

Step 2: Exclude SQL Server Files from Antivirus/Backup Scanning

  • Open your antivirus console (e.g., Windows Defender) and add exclusions for the SQL data, log, and tempdb directories.
  • For Windows Defender via PowerShell:
  Add-MpPreference -ExclusionPath "D:\SQLData\MSSQL16.MSSQLSERVER\MSSQL\DATA"
  Add-MpPreference -ExclusionExtension ".mdf",".ldf",".ndf"
  • Temporarily pause any third-party backup agents (e.g., Veeam, Commvault) and retry the operation to rule out file-locking conflicts.

Step 3: Check Disk Health and File System Compatibility

  • Run chkdsk D: /f /r on the volume hosting the database files (requires a reboot if the volume is in use).
  • If using ReFS, confirm it is formatted with 64K cluster size, as SQL Server 2025 strict-alignment checks may conflict with default 4K cluster ReFS volumes.
  • Review the Windows Event Viewer under Applications and Services Logs > Microsoft > Windows > Storage for correlating disk-level I/O errors.

Step 4: Update Storage Drivers and SQL Server Cumulative Update

  • Open Device Manager, locate your storage controller, and update to the latest manufacturer driver.
  • Install the latest SQL Server 2025 Cumulative Update (CU) from Microsoft, as several concurrent I/O fixes for Windows Server 2025 storage stacks are addressed in CU patches.
  • Restart the SQL Server service after installation: Restart-Service MSSQLSERVER.

Alternative or Verification Steps

  • Re-run the operation that triggered the error (e.g., database snapshot, backup, or file growth) and confirm it completes without Error 5143 in the SQL Server error log (ERRORLOG file in the LOG directory).
  • If the issue persists, disable Instant File Initialization temporarily (remove SE_MANAGE_VOLUME_NAME privilege from the service account) to test whether the error is specifically tied to sparse file handling, then re-enable once the storage/driver issue is resolved.