Raid 4, Raid 5, Raid 1 – Dell PowerEdge 4400 User Manual
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The set of diskettes from which you can perform a complete installation of an application program. When you reconfigure a program, you often
need its program diskette set.
protected mode
An operating mode supported by 80286 or higher microprocessors, protected mode allows operating systems to implement:
l
A memory address space of 16 MB (80286 microprocessor) to 4 GB (Intel386 or higher microprocessor)
l
Multitasking
l
Virtual memory, a method for increasing addressable memory by using the hard-disk drive
The Windows NT 32-bit operating system runs in protected mode. MS-DOS cannot run in protected mode; however, some programs that you can
start from MS-DOS
—such as Windows—are able to put the computer into protected mode.
PS/2
Abbreviation for Personal System/2.
PSPB
Abbreviation for power-supply paralleling board.
PVC
Abbreviation for polyvinyl chloride.
Q
QIC
Abbreviation for quarter-inch cartridge.
R
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 also
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 also
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 also
.
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 also
RAID 10