RAID Technology Overview - September 2007

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 HP Smart Array Controllers are as follows:
• RAID 0
• RAID 1+0
• RAID 5
• ADG
Physical Disks and Logical Drives
The group of physical disks containing the logical drive is called an array (or drive array). Since
all the physical disks in an array are commonly configured into a single logical drive, the term
array is also used as a synonym for logical drive.
In this document, “disk” refers to a physical disk, and “drive” refers to a logical drive or array.
12 Introduction to RAID Technology