Mylex DAC960PG, Installation Manual

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Glossary
Manual No. 771971 Glossary-5
RAID
RAID stands for Redundant Array of Independent Disks. The DAC960PG
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 DAC960 Series 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% 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 XOR redundancy.
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)