A legacy SQL Server high-availability feature that maintains a synchronized copy of a database on a secondary server, replaced by Always On Availability Groups in modern SQL Server versions.
- Database Mirroring was deprecated beginning with SQL Server 2012 and removed from SQL Server 2022: Organizations still running it should plan migration to Always On Availability Groups.
- Mirroring operated in three modes: High Safety with Automatic Failover (synchronous and requires a witness), High Safety without Automatic Failover (synchronous with manual failover), and High Performance (asynchronous).
- Unlike Always On Availability Groups, Database Mirroring only supports a single mirror database: It does not support readable secondaries or multiple replicas.
- DBAs maintaining legacy SQL Server environments (2008–2014) may still manage mirrored databases: Monitoring can be performed using SQL Server Management Studio (SSMS) Database Mirroring Monitor or dynamic management views such as
sys.database_mirroring. - Related terms: Always On Availability Groups, Log Shipping, High Availability, Failover.
