Users Guide

Abbreviation for power-supply paralleling board.
PVC
Abbreviation for polyvinyl chloride.
QIC
Abbreviation for quarter-inch cartridge.
RAID
Acronym for redundant arrays of independent disks. This phrase was introduced by David Patterson, Garth Gibson, and
Randy Katz at the University of California at Berkeley in 1987. The goal of RAID is to use multiple small, inexpensive
disk drives to provide high storage capacity and performance while maintaining or improving the reliability of the disk
subsystem.
Patterson, Gibson, and Katz described five different methods, which are known as RAID levels 1 through 5. Each level
uses one or more extra drives to provide a means of recovering data lost when a disk fails, so that the effective failure
rate of the whole disk subsystem becomes very low.
RAID 0
RAID 0 is commonly called striping. This was not originally defined as a RAID level but has since come into popular
use. In this array configuration, data is written sequentially across the available disks and no redundancy is provided.
RAID 0 configurations provide very high performance but relatively low reliability. RAID 0 is the best choice when
controller cards are duplexed. See also striping.
RAID 1
RAID 1 is commonly called mirroring. RAID 1 also uses striping, so RAID 1 may be regarded as the mirroring of
RAID 0 configurations. RAID 1 is the best choice in high-availability applications that require high performance or
relatively low data capacity. See also mirroring, RAID 10, striping.
RAID 4
RAID 4 is commonly called guarding. It uses data striping, like RAID 0, but adds a single, dedicated parity drive. The
parity data stored on this drive can be used to recover data lost from a single failed drive. RAID 4 configurations write
data slowly because parity data has to be generated and written to the parity drive, and the generation of the parity data
frequently requires reading data from multiple physical drives. See also guarding and striping.
RAID 5
RAID 5, like RAID 4, is commonly called guarding. RAID 5 is identical to RAID 4, except that the parity data is
distributed evenly across all physical drives instead of a parity drive. In configurations using a large number of physical
drives in which a large number of simultaneous small write operations are being performed, RAID 5 offers potentially
higher performance than RAID 4. RAID 4 and RAID 5 configurations are appropriate in high-availability applications
where performance is less critical or where high data capacity is required. See also guarding.
RAID 10
RAID 10 is a mirroring technique in which data is duplicated across two identical RAID 0 arrays or hard-disk drives.
All data on a physical drive in one array is duplicated, or mirrored , on a drive in the second array. Mirroring offers