How to fix Error 3222 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3222 — “WriteFileEx System Function Only Wrote N Bytes”

Why This Error Happens

This error occurs when SQL Server 2025 attempts an asynchronous write operation to a database or transaction log file, but the underlying Windows I/O subsystem only partially completes the write due to disk-level interference. The most common root causes are antivirus or backup software intercepting the file handle, disk space exhaustion on the volume, or a failing/corrupted storage controller that cannot sustain the requested write size. In virtualized or SAN-based environments, this can also stem from misconfigured storage timeout settings or an unstable network path to the storage array.

Step-by-Step Resolution Guide

Step 1: Exclude SQL Server Files from Antivirus and Backup Agents

  • Open your antivirus/EDR console and add exclusions for *.mdf, *.ldf, *.ndf, and the SQL Server binary directory (typically C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\).
  • Disable any third-party VSS-based backup agents during active SQL Server backup windows to prevent file-handle contention.
  • Restart the SQL Server service after applying exclusions: Restart-Service MSSQLSERVER.

Step 2: Verify Disk Space and Volume Health

  • Run Get-PSDrive -PSProvider FileSystem in PowerShell to confirm the target volume has sufficient free space (SQL Server needs headroom for log/data file growth).
  • Use chkdsk D: /f /r (replace D: with your data drive) during a maintenance window to scan for and repair file system corruption.
  • Check Windows Server 2025 Storage Spaces or SAN multipathing (MPIO) health via Get-PhysicalDisk to rule out a degraded disk.

Step 3: Review and Adjust Storage I/O Timeout Settings

  • Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Disk and confirm the TimeOutValue is appropriately set (typically 60 seconds) for SAN-attached storage.
  • If using iSCSI, validate the initiator timeout settings in the iSCSI Initiator Properties under the “Advanced” tab.
  • Coordinate with your storage vendor to confirm firmware and driver versions are current, especially after any recent Windows Server 2025 cumulative updates.

Step 4: Check SQL Server Error Log and Event Viewer for Correlating Events

  • Open SQL Server Management Studio (SSMS) and review SQL Server Logs for repeated 3222 entries and their exact timestamps.
  • Cross-reference Windows Event Viewer (Application and System logs) for Disk (Event ID 51/153) or Ntfs warnings occurring at the same time.
  • If correlating hardware errors are found, escalate to your storage/hardware team before resuming production workloads.

Alternative or Verification Steps

  • Run a manual full backup (BACKUP DATABASE [YourDB] TO DISK = 'D:\Backup\test.bak') and monitor for successful completion without 3222 errors in the SQL error log.
  • If the issue persists after storage and AV remediation, move the affected database files to a different physical volume or LUN as a temporary workaround while hardware diagnostics continue.