Dell 3 User Manual download pdf (Page 244)

242 Glossary

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Parity—Parity is an extra bit added to a byte or word to reveal errors in

storage (in random access memory, 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 hard 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 Drive—A hard drive that stores data. A hard drive consists of one

or more rigid magnetic discs rotating about a central axle with associated

read/write heads and electronics.

Physical Drive 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. An array of multiple

independent hard disk drives that yields better performance than 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.

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Dell 3 User Manual Page 244