Mylex eXtremeRAID Installation Guide download pdf (Page 63)

Glossary

775013 G-5

RAID

RAID stands for Redundant Array of Independent Disks. The DAC1164

controllers implement this technology to connect up to 15 SCSI devices per

channel. Several different forms of RAID implementation have been

defined. Each form is usually referred to as a “RAID level.” All the RAID

levels supported by DAC1164 controllers are shown below.

The appropriate RAID level for a system is selected by the system manager

or integrator. This decision will be based on which of the following are to be

emphasized:

Disk Capacity

Data Availability (redundancy or fault tolerance)

Disk Performance

RAID Levels

The disk array controllers monitored by this utility support four RAID

Advisory Board-approved (RAID 0, RAID 1, RAID 3, RAID 5) and two

special RAID levels (RAID 0+1, and JBOD).

Level 0.

Block “striping” across multiple drives is provided, yielding higher

performance than is possible with individual drives. This level does not

provide any redundancy.

Level 1.

Drives are paired and mirrored. All data is 100 percent duplicated

on a drive of equivalent size.

Level 3.

Data is “striped” across several physical drives. Maintains parity

information which can be used for data recovery.

Level 5.

Data is “striped” across several physical drives. For data

redundancy, drives are encoded with rotated parity.

Level 0+1.

Combines RAID 0 striping and RAID 1 mirroring. This level

provides redundancy through mirroring. (Mylex RAID 6)

JBOD.

Sometimes referred to as “Just a Bunch of Drives.” Each drive is

operated independently like a normal disk controller, or drives may be

spanned and seen as a single drive. This level does not provide data

redundancy. (Mylex RAID 7)

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Mylex eXtremeRAID Installation Guide Page 63