Raid Levels - Novell LINUX ENTERPRISE DESKTOP 10 SP2 - DEPLOYMENT GUIDE 08-05-2008 Deployment Manual

rity, or both. Most RAID controllers use the SCSI protocol because it can address a
larger number of hard disks in a more effective way than the IDE protocol and is more
suitable for parallel processing of commands. There are some RAID controllers that
support IDE or SATA hard disks. Soft RAID provides the advantages of RAID systems
without the additional cost of hardware RAID controllers. However, this requires some
CPU time and has memory requirements that make it unsuitable for real high perfor-
mance computers.

7.2.1 RAID Levels

SUSE® Linux Enterprise offers the option of combining several hard disks into one
soft RAID system with the help of YaST—a very reasonable alternative to hardware
RAID. RAID implies several strategies for combining several hard disks in a RAID
system, each with different goals, advantages, and characteristics. These variations are
commonly known as RAID levels.
Common RAID levels are:
RAID 0
This level improves the performance of your data access by spreading out blocks
of each file across multiple disk drives. Actually, this is not really a RAID, because
it does not provide data backup, but the name RAID 0 for this type of system has
become the norm. With RAID 0, two or more hard disks are pooled together. The
performance is very good, but the RAID system is destroyed and your data lost if
even one hard disk fails.
RAID 1
This level provides adequate security for your data, because the data is copied to
another hard disk 1:1. This is known as hard disk mirroring. If a disk is destroyed,
a copy of its contents is available on another one. All of them except one could be
damaged without endangering your data. However, if damage is not detected, it
also may happen that damaged data is mirrored to the correct disk and data corrup-
tion happens that way. The writing performance suffers a little in the copying process
compared to when using single disk access (10 to 20 % slower), but read access is
significantly faster in comparison to any one of the normal physical hard disks,
because the data is duplicated so can be parallel scanned. Generally it can be said
that Level 1 provides nearly twice the read transaction rate of single disks and almost
the same write transaction rate as single disks.
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