Mirroring is a function of RAID in which data stored on one drive is duplicated on another drive. This creates redundant identical copies of data. There must be two physical drives in a set. Because data is duplicated to both drives, there is no gain in write speeds.

Advantages to Mirroring

With mirroring, if one disk fails in a RAID set, the data is still left intact on the remaining drive. Mirroring also increases the read performance of data when compared to a single drive. Data can be read by both disks.