Chapter 1. Introduction to the 3ware Command Line Interface
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: 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 |
|
|
RAID 10 | (number of drives / 2) X (capacity of smallest drive) |
|
|
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 down to 120 GB. For more information, see the discussion of drive coercion under “Creating a Hot Spare” on page 42.
14 | 3ware Serial ATA RAID Controller CLI Guide for the Power Mac G5 |
