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MegaRAID Enterprise 1600 Hardware Guide
132
Glossary,
Continued
Mapping
The conversion between multiple data addressing schemes, especially conversions between
member disk block addresses and block addresses of the virtual disks presented to the operating
environment by Array Management Software.
MB
(Megabyte) An abbreviation for 1,000,000 (10 to the sixth power) bytes. It is the same as 1,000
KB (kilobytes).
Multi-threaded
Having multiple concurrent or pseudo-concurrent execution sequences. Used to describe processes
in computer systems. Multi-threaded processes allow throughput-intensive applications to
efficiently use a disk array to increase I/O performance.
Operating Environment
The operating environment includes the host computer where the array is attached, any I/O
buses and adapters, the host operating system, and any additional software required to operate the
array. For host-based arrays, the operating environment includes I/O driver software for the
member disks, but does not include Array Management Software, which is regarded as part of the
array itself.
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.
Cont’d