Database mirroring is a SQL Server high availability solution provided by Microsoft, with the following components.
- Principal database server: a source database that you configure for the mirroring.
- Mirror database server: a destination database that you must restore with NORECOVERY. Ideally, a mirrored database should be on a separate server.
- Witness Server: an optional component that you can set up to configure the mirror with automatic failover.
- Endpoint: the communication medium used by the principal and mirror server. The mirror listens on port number 5022; however, you can change it during the configuration.