AMCC 3WARE 720-0138-00 - Manual (Page 18)

Chapter 2. Introducing the 3ware® 9590SE-4ME RAID Controller
10 3ware Serial ATA RAID Controller User Guide for the Power Mac G5
Determining What RAID Level to Use
Your choice of which type of RAID unit (array) to create will depend on your
needs. You may wish to maximize speed of access, total amount of storage, or
redundant protection of data. Each type of RAID unit offers a different blend
of these characteristics.
The following table provides a brief summary of RAID type characteristics.
You can create one or more units, depending on the number of drives you
have installed.
Using Drive Capacity Efficiently
To make the most efficient use of drive capacity, it is advisable to use drives
of the same capacity. This is because the capacity of each drive is limited to
the capacity of the smallest drive in the unit.
The total array capacity is defined as follows:
Table 3: RAID Configuration Types
RAID Type Description
RAID 0 Provides performance, but no fault tolerance.
RAID 1 Provides fault tolerance and a read speed advantage over non-
RAID disks.
RAID 5 This type of unit provides performance, fault tolerance, and high
storage efficiency.
RAID 10 A combination of striped and mirrored units for fault tolerance
and high performance.
Single Disk Not a RAID type, but supported as a configuration.
Provides for maximum disk capacity with no redundancy.
Table 4: Drive Capacity
RAID Level Capacity
Single Disk capacity of the drive
RAID 0 (number of drives) X (capacity of the smallest drive)
RAID 1 capacity of the smallest drive
RAID 5 (number of drives - 1) X (capacity of the smallest drive)
Storage efficiency increases with the number of disks:
storage efficiency = (number of drives -1)/(number of drives)
RAID 10 (number of drives / 2) X (capacity of smallest drive)