Dell PowerVault 715N User Manual page 27

An I/O port used most often to connect a parallel printer to your system. You can usually identify a parallel port on your
system by its 25-hole connector.
PCI
Abbreviation for Peripheral Component Interconnect. A standard for local-bus implementation developed by Intel
Corporation.
peripheral device
An internal or external device—such as a printer, a hard drive, or a keyboard—connected to a system.
POST
Acronym for power-on self-test. Before the operating system loads when you turn on your system, the POST tests various
system components such as RAM, the hard drives, and the keyboard.
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 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 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 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 guarding.
RAID 10
RAID 10 is a mirroring technique in which data is duplicated across two identical RAID 0 arrays or hard drives. All data on
a physical drive in one array is duplicated, or mirrored, on a drive in the second array. Mirroring offers complete
redundancy of data for greater data security. See mirroring, RAID 1, and striping.