Definition of mirroring

Immediately reproducing every update to a read-write database (the principal database) onto a read-only mirror of that database (the mirror database) residing on a separate instance of the database engine (the mirror server). In production environments, the mirror server is on another machine. The mirror database is created by restoring a full backup of the principal database (without recovery).

In a storage sense, ‘mirroring’ refers to duplicating data on multiple disk storage devices to provide backup in the event of a system failure.

In an Internet sense, ‘mirroring’ refers to replicating the contents of a Web site at another site to minimize load on the main server, or to speed up connectivity in a specific geographic region.