Word for the Day Archive

RAID

An acronym for Redundant Array of Independent Disks. Sometimes you will see the word Inexpensive in place of Independent, but the basic point is the same: Multiple drives doing the work of one drive, but with redundancy. The term was coined in 1987 by researchers at the University of California at Berkeley to describe a series of redundant architectures used in fault-tolerant disk arrays (RAID levels 1 through 5). It was originally developed as a way to organize small format disk storage devices to dramatically increase input/output (I/O) speed and improve data availability. At its simplest, a RAID-1 array consists of two drives that store identical information. If one drive goes down, the other continues to work, resulting in no downtime for users. RAID-1 isn't a very efficient way to store data, however. To save disk space, RAID-3, -4, and -5 "stripe" data and parity information across multiple drives (RAID-3 and -4 store all parity data on a single drive). If a single disk fails, the parity information can be used to rebuild the lost data. Unfortunately, there is a performance trade-off: depending on the RAID type used, a RAID will be slower than a single drive at either reading or writing data. In demanding audio or video applications, however, a properly configured RAID system can actually increase bandwidth (speed) while improving reliability.