AMCC 720-0138-00 manual Determining What RAID Level to Use, Using Drive Capacity Efficiently

Chapter 2. Introducing the 3ware® 9590SE-4ME RAID Controller

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.

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.

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 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)

10 3ware Serial ATA RAID Controller User Guide for the Power Mac G5