Using Drive Capacity Efficiently

Because the capacity of each drive is limited to the capacity of the smallest drive in the unit, use drives of the same capacity in a unit.

The total unit capacity is defined as follows:

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)

Through drive coercion, the capacity used for each drive is rounded down to improve the likelihood that you can use drives from differing manufactures 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 is rounded down to 44 GB, and a 123-GB drive is rounded down to 120 GB.


	Note: All drives in a unit must be of the same type, either SAS or SATA.

Related Topics: RAID Concepts; Available RAID Configurations