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RAID
(redundant array of independent discs) is a concept
in storage subsystems that can deliver higher levels
of protection against down-time and data loss than conventional
disc drives. RAID refers to a drive architecture designed
to safeguard critical data through redundancy. In theory,
RAID arrays composed of conventional discs can function
for hundreds or even thousands of years without losing
data because of a disc failure. RAID also offers other
benefits: it can improve input/output performance, make
servicing simpler and quicker and allow users to fine-tune
the drive system to match the needs of specific applications.
The following standard RAID specifications will be used
here:
RAID 0:Non-redundant
striped array: drives are accessed alternatively, as
of stacked one on top of the other.
RAID 1:
Mirrored arrays: information written to one disk is
also written to another simultaneously.
RAID 5: Parity
data used to apply data correction for data recovery
is striped across all drives within the RAID group for
increased performance.
RAID 10:Striped
array of mirroring.
RAM
Acronym
for random access memory. An integrated circuit memory
chip that allows information to be stored and retrieved
by a microprocessor or controller.
RLL
Acronym for run length limited. A method used on some
hard disks to encode data into magnetic pulses. RLL
requires more processing, but stores almost 50 percent
more data per disk than the older MFM (modified frequency
modulation) method.
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