Microsoft® SQL Server 2012 Unleashed

What Is Database Mirroring?

When you mirror a database, you are essentially asking for a complete copy of a database to be created and maintained, with as much up-to-the-second completeness as possible; you are asking for a mirror image. Database mirroring is a database-level feature. This means that there is no support for filtering, sub-setting, or any form of partitioning. You mirror a complete database or nothing at all. This limitation actually keeps database mirroring simple and clean to implement. It also certainly provides some drawbacks, such as burning up twice the amount of disk storage, but what you get in return is well worth the cost in storage.

Database mirroring works through the transaction log of the principal database (of ...