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Chapter 2 - AN INTRODUCTION TO RAID
2.1 RAID VOLUMES
RAID technology allows one or more disks to be combined into a logical volume which provides greater performance
and/or protection than standard single disk drives. These volumes, also known as RAID Groups, appear like regular disk
drives to the operating system and can be partitioned, formatted and used just like any other normal disk. The creation and
necessaries calculation of the RAID is hidden from the operating system.
There are several different methods of combining disks. Each method is referred to as a RAID “level” such as RAID Level 1,
or RAID 1. The details of each level are summarized below and detailed in the following sections.
RAID LEVEL CONFIGURED
AS
ADVANTAGES DISADVANTAGES
0 Striped Excellent performance
All of the Hard Drive disk space
is available to use
No data protection
1 Mirrored Excellent data protection Space available is divided by half
10 Mirrored Striped High performance
Excellent data protection
Space available is divided by
half.
Required 4 disk or more
5 Parity RAID Good data protection, Good
Proformance
Some performance degradation
for writes.
Space avalible is total number of
hard drive space minus one
hard drive space
Required 3 disk or more
Combination Concatenated Good performance
All of the Hard Drive disk space
is available to use
No data protection
Single Drive / Segment Contiguous Same as single disk Same as single disk
2.2 SEGMENTING DISKS
For increased versatility, the TR4M utitly, SATARAID5 software, allows individual disks to be divided into smaller segments
which can then be combined into different volumes. As an example, if a user has one set of data that must be protected at
all costs, another set of data which should be protected at reasonable cost and another set that doesn’t need any
protection at all; the user can divide three disks into sections as shown in Figure 1. The yellow regions define the high
security volume, the green section is the middle security volume and the light blue shows the unprotected area.
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