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Understanding RAID Concepts and Levels

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Using Drive Capacity Efficiently

To make the most efficient use of drive capacity, it is advisable to use drives

of the same capacity in a unit. This is because the capacity of each drive is

limited to the capacity of the smallest drive in the unit.

The total unit capacity is defined as follows:

Through drive coercion, the capacity used for each drive is rounded down so

that drives from differing manufacturers are more likely to be able to be used

as spares for each other. The capacity used for each drive is rounded down to

the nearest GB for drives under 45 GB (45,000,000,000 bytes), and rounded

down to the nearest 5 GB for drives over 45 GB. For example, a 44.3 GB

drive will be rounded down to 44 GB, and a 123 GB drive will be rounded

5RAID 6

RAID 5 with hot spare

RAID 10 with hot spare

Combination of RAID 0, RAID 1, hot spare, single disk

6 or more RAID 6

RAID 6 with hot spare

RAID 50

Combination of RAID 0, 1, 5, 6,10, hot spare, single disk

Table 4: Possible Configurations Based on Number of Drives

# Drives Possible RAID Configurations

Table 5: 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 6 (number of drives - 2) x (capacity of the smallest drive)

RAID 10 (number of drives / 2) X (capacity of smallest drive)

RAID 50 (number of drives - number of groups of drives) X (capacity of the

smallest drive)

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 360 361

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AMCC 3ware 9650SE-2LP Guía de usuario Pagina 25