LSI MegaRAID Express 500 - Manual (Page 27)

Chapter 2 Introduction to RAID 13
Disk Mirroring
With mirroring (used in RAID 1), data written to one disk drive is simultaneously written
to another disk drive. If one disk drive fails, the contents of the other disk drive can be
used to run the system and reconstruct the failed drive. The primary advantage of disk
mirroring is that it provides 100% data redundancy. Since the contents of the disk drive
are completely written to a second drive, it does not matter if one of the drives fails. Both
drives contain the same data at all times. Either drive can act as the operational drive.
Disk mirroring provides 100% redundancy, but is expensive because each drive in the
system must be duplicated.