Benefits of mirroring

If media failure occurs, mirroring provides the database server administrator with a means of recovering data without taking the database server offline. This feature results in greater reliability and less system downtime. Furthermore, applications can continue to read from and write to a database whose primary chunks are on the affected media, provided that the chunks that mirror this data are located on separate media.

Any critical database must be located in a mirrored dbspace. The root dbspace, which contains the database server reserved pages, must be mirrored.