HP A7143A RAID160 SA Controller Support Guide

RAID Technology Overview
What is RAID?
Chapter 114
published, if a disk drive crashed data restoration was typically
dependent on backup from a tape drive. In addition, the system would
have to be taken off-line to replace the failed disk.
The RAID Concept
The RAID study proposed a multi-level concept for improved data
input/output performance (arrays with logical drives) and improved data
availability (by avoiding the impact of disk drive failures). Five original
RAID configurations, or “levels” (RAID 1 through RAID 5), were defined
to meet the needs of various computing environments.
As the five original RAID configurations progress from RAID 1 through
RAID 5, data redundancy increases. Each RAID configuration offers
greater fault tolerance than the RAID configuration that precedes it.
Overall, a RAID has three main attributes that are exploited in some
way by all of the five original RAID configurations and by most of the
other RAID configurations that have been defined since the RAID study
was published in 1987. They are:
• A set of physical disk drives that can function as one or more logical
drives (improved I/O)
• Data distribution across multiple physical disks (striping)
• Data recovery or reconstruction of data in the event of a physical disk
failure (redundancy)
One exception is RAID 0. The term “RAID 0” was adopted to describe a
disk array configuration that includes data block striping, but lacks
redundancy.
Since the publication of the RAID study, RAID 2, RAID 3 and RAID 4
have become impractical due to technological changes. There are other
RAID configurations (some are proprietary) that have been defined over
the years, but a detailed description of all RAID configurations is beyond
the scope of this document. The RAID configurations that are supported
by the HP RAID160 SA controller (0, 1+0, 5, and ADG) are detailed in
“HP RAID160 SA Controller Supported RAID Configurations” on
page 19.