HP A7143A RAID160 SA Controller Support Guide

RAID Technology Overview
What is RAID?
Chapter 1 13
What is RAID?
The RAID concept was proposed in 1987 when “A Case for Redundant
Arrays of Inexpensive Disks (RAID)” was published by David Patterson,
Garth Gibson, and Randy Katz at the University of California, Berkeley.
This study defined five different disk array configurations, or RAID
levels. All of the RAID levels provided fault tolerance and each RAID
level offered different feature sets and performance, to accommodate
different systems administration priorities and computing
environments. The idea was to combine multiple, small, inexpensive,
disk drives into an array that would function as a single logical drive,
but provide better performance than a single large expensive disk drive
(SLED).
NOTE Currently, RAID stands for “Redundant Array of Independent Disks”,
because, in general, disks have become inexpensive.
Small disk drives are lower in performance and have less capacity, when
compared to large disk drives. Small drives also have lower storage
density than large drives, but small drives are equal to or better than
large drives in four areas:
• I/O per actuator (multiple I/O capability)
• Cost per megabyte
• Mean time between failures (MTBF)
• SCSI controller per disk drive (better cost/performance ratio)
Grouping small disk drives into an array provides:
• High transfer rates
• Increased disk capacity
•High I/O rates
The RAID study pointed out that as the number of disk drives in an
array (also referred to as a stripe set) increases, the mean time between
failures (MTBF) of the array decreases. At the time the RAID study was