How to fix Error 1485 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 1485 (Database Mirroring Deprecated Feature Notice)

Why This Error Happens

Error 1485 occurs because Database Mirroring is a deprecated feature in modern SQL Server releases, and SQL Server 2025 raises this warning whenever mirroring is enabled on an instance to alert administrators that the feature is scheduled for removal. This typically happens when a database is restored from an older backup with mirroring metadata intact, or when legacy scripts/configurations attempt to invoke ALTER DATABASE ... SET PARTNER or sp_configure settings tied to mirroring endpoints. The error is not a functional failure but a compliance/compatibility notice indicating your architecture relies on an unsupported high-availability mechanism.

Step-by-Step Resolution Guide

Step 1: Identify Mirroring Dependencies

  • Open SQL Server Management Studio (SSMS) and run SELECT * FROM sys.database_mirroring WHERE mirroring_state IS NOT NULL; to list all databases with active mirroring sessions.
  • Check SQL Server Error Log (via EXEC sp_readerrorlog) for the exact timestamp and database name associated with Error 1485.
  • Review any legacy PowerShell or T-SQL deployment scripts for ALTER DATABASE SET PARTNER or ALTER DATABASE SET WITNESS commands.

Step 2: Migrate to Always On Availability Groups

  • Since mirroring is deprecated, plan a migration to Always On Availability Groups (AG), which is the supported replacement in SQL Server 2025.
  • Enable the Always On Availability Groups feature via SQL Server Configuration Manager: navigate to SQL Server Services > [Your Instance] > Properties > Always On Availability Groups tab, and check “Enable Always On Availability Groups.”
  • Restart the SQL Server service for the change to take effect (net stop MSSQLSERVER followed by net start MSSQLSERVER, or via Services.msc on Windows Server 2025).
  • Use the “New Availability Group Wizard” in SSMS to recreate your HA topology using the previously mirrored databases as primary replicas.

Step 3: Remove Legacy Mirroring Configuration

  • Once failover protection is re-established via AG, break the existing mirroring session by running ALTER DATABASE [YourDB] SET PARTNER OFF; on the principal server.
  • Drop any orphaned mirroring endpoints using DROP ENDPOINT [Mirroring_Endpoint_Name]; to prevent the instance from re-triggering Error 1485 on restart.
  • Verify no mirroring-related extended events sessions are still running by checking sys.server_event_sessions.

Step 4: Suppress or Acknowledge the Warning (Temporary Workaround)

  • If immediate migration to Always On AG isn’t feasible, acknowledge the deprecation notice is logged for compliance tracking only and does not block mirroring functionality in this release.
  • Document the planned migration timeline in your change management system, since mirroring support may be fully removed in a future cumulative update.

Alternative or Verification Steps

  • Verify the fix by querying sys.database_mirroring again post-migration — it should return no active mirroring states, and sys.dm_hadr_availability_group_states should show your new AG as “Healthy.”
  • As an alternative, if Always On AG is not licensed in your SQL Server edition, consider Log Shipping as a lower-complexity, officially supported fallback for disaster recovery instead of mirroring.