Overview 15
About RAID
RAID is a group of multiple independent physical disks that provide high
performance or better data availability by increasing the number of drives
used for saving and accessing data. A RAID disk subsystem improves
I/O performance and data availability. The physical disk group appears to the
host system as a single storage unit. Data throughput improves because
multiple disks can be accessed simultaneously. RAID systems also improve
data storage availability and fault tolerance.

RAID Levels

• RAID 0 uses disk striping to provide high data throughput, especially for
large files in an environment that requires no data redundancy.
• RAID 1 uses disk mirroring so that data written to one physical disk is
simultaneously written to another physical disk. This is good for small
databases or other applications that require small capacity, but complete
data redundancy.
• RAID 10, a combination of RAID 0 and RAID 1, uses disk striping
across mirrored disks. It provides high data throughput and complete
data redundancy.
CAUTION: Lost data on a RAID 0 disk cannot be recovered in the event of
aphysical disk failure.
RAID Terminology

RAID 0

RAID 0 allows you to write data across multiple physical disks instead of just
one physical disk. RAID 0 involves partitioning each physical disk storage space
into 64 KB stripes. These stripes are interleaved in a repeated sequential
manner. The part of the stripe on a single physical disk is called a stripe
element.
For example, in a four-disk system using only RAID 0, segment 1 is written to
disk 1, segment 2 is written to disk 2, and so on. RAID 0 enhances
performance because multiple physical disks are accessed simultaneously, but
it does not provide data redundancy. Figure2-2 shows an example of RAID 0.
PERC H200.book Page 15 Tuesday, July 13, 2010 4:15 PM