How to fix Error 3103 on Windows Server 2025 / Windows 11

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Why This Error Happens

This error occurs when a restore command attempts to bring a secondary filegroup or file online without first establishing a partial restore sequence on the primary filegroup. SQL Server 2025 requires that the very first RESTORE DATABASE statement in a piecemeal restore explicitly include the PARTIAL keyword alongside the primary filegroup. Without this initial flag, the engine has no “anchor point” for subsequent filegroup restores, causing it to reject the sequence entirely.

Step-by-Step Resolution Guide

Step 1: Verify the Backup Set Structure

  • Open SQL Server Management Studio (SSMS) 21 or Azure Data Studio connected to your Windows Server 2025 instance.
  • Run RESTORE FILELISTONLY FROM DISK = 'C:\Backups\YourDB.bak'; to confirm which filegroups exist (PRIMARY, FG_Secondary, etc.).
  • Confirm you know the exact logical file name of the Primary filegroup before proceeding.

Step 2: Restart the Restore Sequence Correctly

  • Drop or stop the current broken restore attempt using RESTORE DATABASE YourDB WITH RECOVERY; only if you intend to abandon the piecemeal restore.
  • If starting fresh, run the initial restore using the mandatory syntax:
  RESTORE DATABASE YourDB
  FILEGROUP = 'PRIMARY'
  FROM DISK = 'C:\Backups\YourDB.bak'
  WITH PARTIAL, NORECOVERY;
  • Ensure NORECOVERY is used here, not RECOVERY, so the database remains in a restoring state for the next files.

Step 3: Restore Secondary Filegroups in Order

  • Once the Primary filegroup restore with PARTIAL succeeds, run subsequent commands for secondary filegroups:
  RESTORE DATABASE YourDB
  FILEGROUP = 'FG_Secondary'
  FROM DISK = 'C:\Backups\YourDB.bak'
  WITH NORECOVERY;
  • Do not include the PARTIAL keyword again in this step—it is only valid on the very first statement of the sequence.

Step 4: Check File System Permissions

  • Navigate to the backup directory (e.g., C:\Backups\) and verify the SQL Server service account (NT Service\MSSQLSERVER or custom domain account) has Read/Write access.
  • In Windows Server 2025, open Server Manager > Tools > Local Security Policy to confirm the service account isn’t blocked by a Group Policy restricting disk I/O operations.

Step 5: Finalize Recovery

  • Once all required filegroups are restored, bring the database online with:
  RESTORE DATABASE YourDB WITH RECOVERY;
  • This closes the partial restore sequence and makes the database accessible.

Alternative or Verification Steps

  • Run SELECT name, state_desc FROM sys.databases WHERE name = 'YourDB'; to confirm the state has changed from RESTORING to ONLINE.
  • If the error persists, use sp_helpfile and RESTORE HEADERONLY to cross-check that the backup file isn’t corrupted or truncated, and re-run the sequence from Step 2 using a verified .bak copy.