How to fix Error 3644 on Windows Server 2025 / Windows 11

by

Why This Error Happens

Error 3644 with the “Prefaulter task failed” message typically occurs when SQL Server 2025’s database engine attempts to pre-allocate or “pre-fault” memory pages for a data file during startup or recovery, but the underlying I/O subsystem returns an unexpected error code. This is most commonly caused by file system permission restrictions on the SQL Server service account, disk-level corruption on the volume hosting the .mdf/.ndf/.ldf files, or a conflict with antivirus/EDR software intercepting file handle operations. In rarer cases, this surfaces when the file resides on a network share or storage tier that does not fully support the sparse file or instant file initialization APIs required by the prefaulting mechanism.

Step-by-Step Resolution Guide

Step 1: Verify File and Folder Permissions

  • Open File Explorer and navigate to the SQL Server data directory (commonly C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA).
  • Right-click the affected file, go to Properties > Security, and confirm the SQL Server service account (e.g., NT Service\MSSQLSERVER) has Full Control.
  • If permissions are missing, run the following in an elevated PowerShell prompt:
icacls "C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\yourfile.mdf" /grant "NT SERVICE\MSSQLSERVER:(F)"

Step 2: Check Disk Health and File Integrity

  • Run chkdsk C: /f /r from an elevated Command Prompt and schedule a restart if the volume is locked.
  • Inspect the Windows Event Viewer under Windows Logs > System for Disk or Ntfs warnings correlating with the SQL error timestamp.
  • If corruption is confirmed, restore the affected database file from the most recent verified backup using RESTORE DATABASE ... WITH REPLACE.

Step 3: Exclude SQL Server Paths from Antivirus/EDR Scanning

  • Open your antivirus console (Windows Defender or third-party) and add exclusions for:
  • The SQL data directory (...\MSSQL\DATA)
  • The SQL log directory (...\MSSQL\LOG)
  • sqlservr.exe process itself
  • Restart the SQL Server (MSSQLSERVER) service via services.msc to apply changes immediately.

Step 4: Confirm Instant File Initialization (IFI) and Storage Compatibility

  • Ensure the SQL Server service account has the Perform Volume Maintenance Tasks right via secpol.msc > Local Policies > User Rights Assignment.
  • If the file resides on a network share, migrate it to local NVMe/SSD storage, as prefaulting operations are not reliably supported on all remote file systems.

Alternative or Verification Steps

  • After applying fixes, restart the SQL Server service and check the SQL Server Error Log (ERRORLOG file) for recurrence of Error 3644; also run DBCC CHECKDB on the affected database to confirm no residual corruption.
  • If the issue persists, temporarily disable instant file initialization via sp_configure and test a clean restart — if the error disappears, the root cause is confirmed to be storage/IFI related rather than permissions.