Database mirroring was first officially supported with SQL Server 2005 SP1. Database mirroring is available in Enterprise and Developer Editions and with some restrictions in Standard and Business Intelligence Editions. Developer Edition can be used only for development purposes and not for production.
The basic concept of database mirroring is simple. Database mirroring maintains a hot standby database (mirror database) kept in sync with the production database (principal database) by transferring transaction log records from the principal database to a mirror database over the network, either synchronously or asynchronously. In case of a failure, the mirror database can be quickly accessed by the clients. Database mirroring has the following benefits: