3Ware 9550SXU-12 User Guide - Page 25

Understanding RAID Concepts and Levels Table 4: Possible Configurations Based on Number of Drives # Drives 5 6 or more Possible RAID Configurations RAID 6 RAID 5 with hot spare RAID 10 with hot spare Combination of RAID 0, RAID 1, hot spare, single disk RAID 6 RAID 6 with hot spare RAID 50 Combination of RAID 0, 1, 5, 6,10, hot spare, single disk 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: Table 5: Drive Capacity RAID Level Single Disk RAID 0 RAID 1 RAID 5 RAID 6 RAID 10 RAID 50 Capacity Capacity of the drive (number of drives) X (capacity of the smallest drive) Capacity of the smallest drive (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) (number of drives - 2) x (capacity of the smallest drive) (number of drives / 2) X (capacity of smallest drive) (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 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 www.3ware.com 13