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RAID User's Guide

Intel ICH7R SATA RAID

1. Introduction

RAID (Redundant Array of Independent Disks) is a method of combining two hard

disk drives into one logical unit. The advantage of an Array is to provide better

performance or data fault tolerance. Fault tolerance is achieved through data re-

dundant operation, where if one drives fails, a mirrored copy of the data can be

found on another drive. This can prevent data loss if the operating system fails or

hangs. The individual disk drives in an array are called members. The configura-

tion information of each member is recorded in the reserved sector. That identifies

the drive as a member. All disk members in a formed disk array are recognized as

a single physical drive to the operating system.

Hard disk drives can be combined together through a few different methods. The

different methods are referred to as different RAID levels. Different RAID levels

represent different performance levels, security levels and implementation costs.

RAID 0 (Striping)

RAID 0 reads and writes sectors of data interleaved between multiple drives. If any

disk member fails, it affects the entire array. The disk array data capacity is equal

to the number of drive members times the capacity of the smallest member. The

striping block size can be set from 4KB to 128KB. RAID 0 does not support fault

tolerance.

RAID 1 (Mirroring)

RAID 1 writes duplicate data onto a pair of drives and reads both sets of data in

parallel. If one of the mirrored drives suffers a mechanical failure or does not

respond, the remaining drive will continue to function. Due to redundancy, the drive

capacity of the array is the capacity of the smallest drive. Under a RAID 1 setup, an

extra drive called the ¡° s pare drive¡± can be attached. Such a drive will be activated to

replace a failed drive that is part of a mirrored array. Due to the fault tolerance, if any

RAID 1 drive fails, data access will not be affected as long as there are other

working drives in the array.