Raid

RAID

(Redundant Array of Independent Disks) A disk subsystem that increases performance or provides fault tolerance or both. RAID uses two or more regular hard drives and a RAID controller, which is plugged into motherboards that do not have RAID circuits. Today, most motherboards have built-in RAID but not necessarily every RAID configuration (see below). In the past, RAID has also been accomplished by software only but was much slower. In the late 1980s, the "I" in RAID stood for "inexpensive" but was later changed to "independent."

In large storage area networks (SANs), floor-standing RAID units are common with terabytes of storage and huge amounts of cache memory. RAID is also used in desktop computers by gamers for speed and by business users for reliability. Following are the various RAID configurations. See NAS and SAN.

RAID 0 - Disk Striping for Performance (Popular)
Widely used for gaming, disk striping interleaves data across multiple drives for performance. However, there are no safeguards against failure. See RAID 0.

RAID 1 - Mirroring for Fault Tolerance (Popular)
Widely used, RAID 1 writes two drives at the same time. It provides the highest reliability but doubles the number of drives needed.

RAID 10 combines RAID 1 mirroring with RAID 0 striping for both safety and performance. See RAID 1 and RAID 10.

RAID 3 - Speed and Fault Tolerance
Data are striped across three or more drives for performance, and parity is computed for safety. Similar to RAID 3, RAID 4 uses block level striping but is not as popular. See RAID 3 and RAID parity.

RAID 5 - Speed and Fault Tolerance (Popular)
Data are striped across three or more drives for performance, and parity is computed for safety. RAID 5 is similar to RAID 3, except that the parity is distributed to all drives. RAID 6 offers more reliability than RAID 5 by performing more parity computations. For more details, see RAID 5.

Big RAID

EMC has been a leader in high-end RAID systems for years with systems storing multiple terabytes of data. (Image courtesy of EMC Corporation.)

Little RAID

Arco was first to provide RAID 1 on IDE drives rather than SCSI. This two-drive unit connected to the motherboard with one cable like a single drive. (Image courtesy of Arco Computer Products, Inc., www.arcoide.com)

Early RAID

This RAID prototype was built by University of Berkeley graduate students in 1992. Housing 36 320MB disk drives, total storage was 11GB. (Image courtesy of The Computer History Museum, www.computerhistory.org)

USB RAID

Super Talent's USB 3.0 RAID drives provide RAID 0 storage that is faster than the internal hard disk. (Image courtesy of Super Talent Technology Corporation, www.supertalent.com)

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RAID [rād]

(computer science)

A group of hard disks that operate together to improve performance or provide fault tolerance and error recovery through data striping, mirroring, and other techniques. Derived from redundant array of inexpensive disks.

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RAID - Redundant Arrays of Independent Disks

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Raid 

a penetration into the enemy rear by mobile tank, mechanized, cavalry, and partisan units for the purpose of inflicting losses; destroying important installations, such as bridges, airfields, railroads, communication lines, warehouses, and supply bases; disrupting the work of supply and evacuation routes; supporting or organizing partisan movements; and diverting enemy forces.

Raids have been used in many wars. The raids by Russian cavalry detachments, such as D. V. Davydov and M. I. Platov’s cossacks in the rear of the French Army in the Patriotic War of 1812, and the large-scale cavalry raids of the Civil War of 1918–20 are well known. During the Great Patriotic War (1941–45) raids were made by Soviet cavalry units, for example, the raid by General P. A. Belov’s cavalry corps in 1942, and by many partisan units.