American Megatrends MegaRAID Express 500 - Manual (Page 110)

MegaRAID Express 500 Hardware Guide 96
Glossary, Continued
Parity Parity is an extra bit added to a byte or word to reveal errors in storage (in RAM
or disk) or transmission. Parity is used to generate a set of redundancy data from
two or more parent data sets. The redundancy data can be used to reconstruct
one of the parent data sets. However, parity data does not fully duplicate the
parent data sets. In RAID, this method is applied to entire drives or stripes across
all disk drives in an array. Parity consists of dedicated parity, in which the parity
of the data on two or more drives is stored on an additional drive, and distributed
parity, in which the parity data are distributed among all the drives in the system.
If a single drive fails, it can be rebuilt from the parity of the respective data on
the remaining drives.
Partition An array virtual disk made up of logical disks rather than physical ones. Also
known as logical volume.
Physical Disk A hard disk drive that stores data. A hard disk drive consists of one or more rigid
magnetic discs rotating about a central axle with associated read/write heads and
electronics.
Physical Disk Roaming The ability of some adapters to detect when hard drives have been moved
to a different slots in the computer, for example, after a hot swap.
Protocol A set of formal rules describing how to transmit data, especially across a
network. Low level protocols define the electrical and physical standards to be
observed, bit- and byte- ordering, and the transmission and error detection and
correction of the bit stream. High level protocols deal with the data formatting,
including the message syntax, the terminal-to-computer dialogue, character sets,
and sequencing of messages.
RAID Redundant Array of Independent Disks (originally Redundant Array of
Inexpensive Disks) is an array of multiple small, independent hard disk drives
that yields performance exceeding that of a Single Large Expensive Disk
(SLED). A RAID disk subsystem improves I/O performance on a server using
only a single drive. The RAID array appears to the host server as a single storage
unit. I/O is expedited because several disks can be accessed simultaneously.
Cont’d