How to fix Error 3246 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3246 — Media Family Marked as Nonappendable

Why This Error Happens

This error occurs when SQL Server 2025 attempts to append a new backup to a backup device or file whose media header indicates that it does not allow appending (nonappendable media). This typically happens when the backup media was originally created with the NOINIT or default appendable settings disabled, or when a third-party backup tool or SQL Server itself wrote a backup set with restricted permissions on the media family. It can also occur if the backup file was created fresh with the FORMAT option, which locks subsequent appends unless explicitly overridden.

Step-by-Step Resolution Guide

Step 1: Identify the Backup Device and Current Media State

  • Open SQL Server Management Studio (SSMS) or run a T-SQL query against the target backup file/device.
  • Execute RESTORE LABELONLY FROM DISK = 'C:\Backups\YourFile.bak' to inspect the media family properties.
  • Confirm whether the Is Appendable flag is set to 0, which confirms the nonappendable state.

Step 2: Reissue the Backup Statement with the INIT Option

  • Modify your BACKUP DATABASE or BACKUP LOG statement to explicitly include WITH INIT.
  • Example command:
  BACKUP DATABASE [YourDatabase] 
  TO DISK = 'C:\Backups\YourFile.bak' 
  WITH INIT, NOFORMAT;
  • Note that INIT overwrites existing backup sets on the media but preserves the media header, whereas FORMAT destroys the entire header.

Step 3: Check File and Folder Permissions on Windows Server 2025

  • Navigate to the backup destination folder (e.g., C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Backup\).
  • Right-click the folder, select Properties > Security, and verify the SQL Server service account (e.g., NT Service\MSSQLSERVER) has Modify and Write permissions.
  • Restart the SQL Server service via services.msc if permissions were changed.

Step 4: Create a New Backup Device if the Issue Persists

  • If the existing media remains locked or corrupted, create a fresh backup device using SSMS under Server Objects > Backup Devices, or run:
  EXEC sp_addumpdevice 'disk', 'NewBackupDevice', 'C:\Backups\NewFile.bak';
  • Point your backup job or maintenance plan to this new device going forward.

Alternative or Verification Steps

  • Run RESTORE VERIFYONLY FROM DISK = 'C:\Backups\YourFile.bak' after applying the fix to confirm the backup file is now readable and valid.
  • If INIT does not resolve the issue, use WITH FORMAT instead to completely reinitialize the media (note: this permanently erases all existing backup sets on that device, so ensure other recovery points exist first).