HP A7143A RAID160 SA Controller Support Guide, February 2007

RAID Technology Overview
What is RAID?
Chapter 1
13
The RAID Concept
The RAID study proposed a multilevel concept for improved data input/output performance (by combining
multiple physical 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.
Overall, RAID has three main attributes that are exploited in some way by all five original RAID
configurations and by most other RAID configurations that have been defined since the 1987 study. These
attributes 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)
“RAID 0” was not defined in the original study, and it does not have all of these attributes. The term was
adopted to describe a disk array configuration that includes data block striping, but lacks redundancy.
RAID 2, RAID 3 and RAID 4 have become impractical due to technological changes. Other RAID
configurations (including some that are proprietary) have been defined over the years as well. You can read
the original RAID study at:
http://techreports.lib.berkeley.edu/accessPages/CSD-87-391.html
RAID configurations supported by the Smart Array 6400 Series Controllers are as follows:
• RAID 0
• RAID 1+0
• RAID 5
•ADG
For more information, see “Smart Array Controller Supported RAID Configurations” on page 16.