RAID stands for Redundant Array of Inexpensive (or
Independent) Disks and is used to group disks into arrays for two reasons: redundancy
and performance. The use of RAID for redundancy is detailed in Chapter 11.
Our focus in this chapter is on the performance aspects of RAID technology.
RAID groups disk drives into arrays to automatically spread I/O operations across
multiple spindles, reducing contention on individual drives. For example, suppose
you place a datafile containing an index on a single drive. If multiple processes use
the index simultaneously, they will all issue I/O requests to the one disk drive, resulting
in contention for the use of that drive.
RAID Basics
RAID disk arrays provide a hardware solution for both reliability and performance.
There are different levels of RAID hardware; the following are most relevant to
performance:
RAID-0
Where availability isn??™t a concern, the disks can be configured as RAID-0, which
is nonredundant disk striping.
RAID-1
Provides the simplest form of redundancy, full duplication of data, which is
referred to as mirroring.
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