How to fix Error 3268 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3268 — Backup Sector Size Mismatch

Why This Error Happens

This error occurs because SQL Server backup files store metadata about the physical sector size of the disk device they were originally written to, and it validates this value during restore operations. When the original backup media (often older disks or specific SAN/NAS configurations) used a different sector size—typically 512 bytes—than the current target device, which may use 4096-byte (4Kn) sectors, SQL Server blocks the restore to prevent data corruption. This mismatch commonly arises when backups are moved between different storage hardware, virtualized disks, or cloud storage accounts with varying Advanced Format disk configurations.

Step-by-Step Resolution Guide

Step 1: Verify the Sector Size of Source and Target Devices

  • Open PowerShell as Administrator and run fsutil fsinfo sectorinfo <DriveLetter>: on both the original and target storage paths.
  • Compare the LogicalBytesPerSector and PhysicalBytesPerSector values to confirm the actual mismatch reported in the error.
  • Note the drive type (SSD, SAN LUN, Azure Disk, etc.) since cloud-based storage often defaults to 4Kn.

Step 2: Restore Using the WITH BLOCKSIZE Override

  • Open SQL Server Management Studio (SSMS) and connect to the target instance.
  • Run the restore command with an explicit block size parameter to force compatibility:
  RESTORE DATABASE [YourDatabase]
  FROM DISK = N'D:\Backups\YourBackup.bak'
  WITH BLOCKSIZE = 65536, REPLACE;
  • If BLOCKSIZE alone does not resolve it, add MAXTRANSFERSIZE = 2097152 to further align I/O operations with the new sector size.

Step 3: Copy the Backup File to a Matching Sector-Size Volume

  • Identify or provision a temporary volume formatted with the same sector size as the original backup (e.g., 512-byte emulation).
  • Use Format-Volume -DriveLetter X -FileSystem NTFS -LogicalSectorSizeBytes 512 (via PowerShell, on supported hardware) or provision a VHD/VHDX with matching sector size using Hyper-V Manager.
  • Copy the .bak file to this intermediary volume and re-attempt the restore from there before moving the restored database to its final production storage.

Step 4: Re-Export the Backup from Source if Possible

  • If the original source server is still accessible, take a fresh BACKUP DATABASE on the source using WITH COMPRESSION to normalize the sector dependency.
  • Transfer this newly created backup file to the Windows Server 2025 target and retry the restore without needing BLOCKSIZE overrides.

Alternative or Verification Steps

  • After applying Step 2 or Step 3, confirm success by checking that RESTORE DATABASE completes without Error 3268 and the database appears as Online in SSMS Object Explorer.
  • As an alternative, mount the backup file via a virtual drive (VHD/VHDX) explicitly created with -LogicalSectorSizeBytes 512 in Hyper-V, which bypasses physical disk sector constraints entirely.