How to fix Error 3271 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3271 — “A Nonrecoverable I/O Error Occurred on File”

Why This Error Happens

Error 3271 occurs when SQL Server’s I/O subsystem fails to read from or write to a database file due to a low-level disk, controller, or filesystem fault that cannot be retried or recovered automatically. This is commonly caused by underlying storage hardware failure, a corrupted NTFS/ReFS volume, antivirus or backup software locking the file, or the storage path becoming unavailable (e.g., disconnected SAN/NAS, dismounted volume). It can also surface during backup or restore operations when the destination device runs out of space or loses connectivity mid-operation.

Step-by-Step Resolution Guide

Step 1: Identify the Affected File and Check SQL Server Error Log

  • Open SQL Server Management Studio (SSMS) and run: EXEC sp_readerrorlog 0, 1, '3271';
  • Note the exact file path (%ls) and the OS-level error message (%ls) reported alongside Error 3271.
  • Cross-reference the timestamp with Windows Event Viewer under Windows Logs > System and Application for Disk, Ntfs, or VDS warnings.

Step 2: Verify Disk and Volume Health

  • Open an elevated Command Prompt and run: chkdsk D: /f /r (replace D: with the actual drive hosting the .mdf/.ldf/.bak file).
  • Check physical disk status via Get-PhysicalDisk | Select DeviceId, HealthStatus, OperationalStatus in PowerShell.
  • If using Storage Spaces or a SAN/NAS, confirm the LUN or virtual disk is online and not in a degraded/predictive-failure state using Server Manager > File and Storage Services.

Step 3: Confirm File Accessibility and Permissions

  • Ensure the SQL Server service account (e.g., NT Service\MSSQLSERVER or a custom domain account) has full read/write permissions on the data folder (typically C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA).
  • Confirm no other process (antivirus, backup agent, or file indexing service) has an exclusive lock on the .mdf/.ndf/.ldf file by checking with Resource Monitor > Disk tab.
  • Add SQL Server data/log directories to your antivirus exclusion list to prevent file-locking conflicts during I/O operations.

Step 4: Restore or Repair the Affected Database

  • If the file is confirmed corrupted and the disk hardware is healthy, take the database offline: ALTER DATABASE [YourDB] SET OFFLINE;
  • Restore from the most recent clean backup: RESTORE DATABASE [YourDB] FROM DISK = 'E:\Backups\YourDB.bak' WITH REPLACE, RECOVERY;
  • If no clean backup exists, attempt DBCC CHECKDB ('YourDB', REPAIR_ALLOW_DATA_LOSS) only as a last resort, after taking a full file-level backup of the current state.

Step 5: Relocate Database Files to Healthy Storage

  • If the underlying volume is failing, move data/log files to a new healthy disk using: ALTER DATABASE [YourDB] MODIFY FILE (NAME = YourDB_Data, FILENAME = 'F:\SQLData\YourDB.mdf');
  • Take the database offline, physically move the files via Move-Item, then bring it back online with ALTER DATABASE [YourDB] SET ONLINE;

Alternative or Verification Steps

  • Run DBCC CHECKDB ('YourDB') WITH NO_INFOMSGS, ALL_ERRORMSGS; to confirm the database is fully consistent and no further I/O errors are logged.
  • Monitor the SQL Server error log and Windows Event Viewer for 24–48 hours post-fix; if Error 3271 recurs on the same physical disk, replace the storage hardware rather than continuing repairs at the software layer.