A fault tolerance technology, also known as RAID 1, whereby data is written simultaneously to two disks, making one disk drive a mirror image of the other. This duplication of all disk information provides data redundancy - if one half of a mirror set fails, the system can continue to operate using the duplicate of the failed disk. Mirror sets are slower than stripe sets with parity for read operations but are faster for write operations.
Mirror sets are often used to provide fault tolerance for the Microsoft Windows NT system partition and boot partition. You can use the Windows NT administrative tool Disk Administrator to create, break, and reestablish mirror sets. In Windows 2000, the corresponding administrative tool is called Disk Management.