If one disk fails, the system is able to use the data from the other disk. Fault tolerance is a reason to use raid 1. If the data on the mirror is primarily used for read access, there is a speed advantage to the mirror single there are two independent copies on two hard drives where a sector can be read. If the data has heavy write characteristics, mirroring will place a performance hit since the data must be written twice. Only Windows NT Server can create and break mirror sets.
Mirrors are file system independent.
Mirrors are not dependent on disk geometry. The only requirement is that free disk space used to place the mirror on be equal to or greater than the size of the primary partition. Primary and mirror partitions must be on separate hard disk drives. They cannot be on the same physical hard disk drive. A single mirror set is limited to two hard disks only.