Understanding RAID Concepts and Levelswww.3ware.com 13Using Drive Capacity EfficientlyTo make the most efficient use of drive capacity, it is advisable to use drivesof the same capacity in a unit. This is because the capacity of each drive islimited 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 sothat drives from differing manufacturers are more likely to be able to be usedas spares for each other. The capacity used for each drive is rounded down tothe nearest GB for drives under 45 GB (45,000,000,000 bytes), and roundeddown to the nearest 5 GB for drives over 45 GB. For example, a 44.3 GBdrive will be rounded down to 44 GB, and a 123 GB drive will be rounded5 RAID 6RAID 5 with hot spareRAID 10 with hot spareCombination of RAID 0, RAID 1, hot spare, single disk6 or more RAID 6RAID 6 with hot spareRAID 50Combination of RAID 0, 1, 5, 6,10, hot spare, single diskTable 4: Possible Configurations Based on Number of Drives# Drives Possible RAID ConfigurationsTable 5: Drive CapacityRAID Level CapacitySingle Disk Capacity of the driveRAID 0 (number of drives) X (capacity of the smallest drive)RAID 1 Capacity of the smallest driveRAID 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 thesmallest drive)
