How to fix Error 4027 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: SQL Server Error 4027 – “Mount tape for %hs of database ‘%ls’ on tape drive ‘%ls'”

Why This Error Happens

This error occurs when SQL Server 2025 initiates a backup or restore operation targeting a physical tape device but cannot proceed because it is waiting for an operator to mount the correct tape volume. The underlying cause is typically that the tape drive is either empty, contains the wrong volume, or the SQL Server Service Account lacks the necessary permissions to communicate with the tape hardware/driver. In some cases, this is also triggered by a misconfigured or orphaned backup device pointing to a non-existent or offline tape resource.

Step-by-Step Resolution Guide

Step 1: Verify Physical Tape Drive Status and Connectivity

  • Check the physical tape drive on the Windows Server 2025 host to ensure it is powered on and connected via the correct SAS/Fibre Channel interface.
  • Open Device Manager on the host and look under “Tape drives” to confirm the OS recognizes the hardware without a yellow warning icon.
  • If the drive is missing, reseat the hardware connection or update the tape drive drivers via the manufacturer’s latest Windows Server 2025 compatible package.

Step 2: Insert or Replace the Correct Tape Media

  • Since this specific error is a “prompt” rather than a hard failure, confirm that a blank or appropriately overwritable tape is physically loaded into the drive.
  • If using a tape library/autoloader, check the magazine slots to ensure the barcode-labeled tape requested by the backup job is actually present in the robotic arm’s accessible queue.
  • Run RESTORE LABELONLY FROM TAPE = '\\.\Tape0' in SQL Server Management Studio (SSMS) to verify the drive can read the currently inserted media header.

Step 3: Validate SQL Server Service Account Permissions

  • Navigate to Services.msc on Windows Server 2025 and locate the “SQL Server (MSSQLSERVER)” service.
  • Ensure the “Log On As” account has been granted Read/Write access to the tape device path (e.g., \\.\Tape0) via local security policy.
  • Add the service account to the local Backup Operators group to ensure it has the SeBackupPrivilege and SeRestorePrivilege rights required to interface with removable storage.

Step 4: Update the Backup Job Configuration

  • If the tape drive has been replaced or renamed in the Windows OS, update the legacy T-SQL script or SQL Agent Job step.
  • Modify the BACKUP DATABASE syntax to reflect the current, active tape drive letter/path:
  BACKUP DATABASE [YourDB] TO TAPE = '\\.\Tape0' WITH NOREWIND, NOUNLOAD;
  • Ensure the NOUNLOAD parameter is used if you intend to keep the tape mounted for sequential multi-database backups to avoid repeated mount prompts.

Alternative or Verification Steps

  • Verification: Once the tape is loaded and permissions are updated, re-run the specific backup job via SQL Server Agent; the job history should show a “Succeeded” status without triggering the Error 4027 mount prompt.
  • Alternative: If physical tape hardware continues to fail intermittently, consider migrating the backup strategy to a Virtual Tape Library (VTL) or standard disk-based backup (TO DISK =) to eliminate physical media handling errors entirely.