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Database mirroring Database Mirroring is the latest addition to the SQL Server availability options. It provides many features that previous options such as Transactional Replication, Clustering, and Log shipping did not provide. However, it is not necessarily the best alternative in all situations and many times the best alternative is to mix more than one HA (High Availability) option, such as Clustering and Database Mirroring. For example, clustering could be used to handle local failover, while Database Mirroring is used to maintain a geographically separate and “hot” copy of a database. Overview Database Mirroring works by maintaining 2 copies of a single database. One copy (called the Principal) is usable just like any other database and the second copy (called the Mirror and residing on a different SQL Server Instance) is in a state where it is constantly receiving changes from the Principal and applying them locally.