3Ware 9550SXU16MLB10 User Guide - Page 19

Understanding RAID Table 2: Possible Configurations Based on Number of Drives # Drives Possible RAID Configurations 6 or more RAID 50 Depending on the number of drives, a RAID 50 may contain from 2 to 4 subunits. For example, with 12 drives, possible RAID 50 configurations include 2 subunits of 6, 3 subunits of 4, or 4 subunits of 3. With 10 drives, a RAID 50 will contain 2 subunits of 5 drives each. Combination of RAID 0, 1, 5, 10, hot spare, and single disk Drive Capacity Considerations The capacity of each drive is limited to the capacity of the smallest drive in the array. The total array capacity is defined as follows: Table 3: Drive Capacity RAID Level Capacity 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) RAID 10 RAID 50 Storage efficiency increases with the number of disks: storage efficiency = (number of drives -1)/(number of drives) (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), and rounded down to the nearest 5 GBytes for drives over 45 GB. For example, a 44.3 GB drive will be rounded down to 44 GBytes, and a 123 GB drives will be rounded. down to 120 GBytes. For more information, see the discussion of drive coercion under "Creating a Hot Spare" on page 92. Support for Over 2 Terabytes Windows 2000, Windows XP, Linux 2.4, and FreeBSD 4.x, do not currently recognize unit capacity in excess of 2 TB. If the combined capacity of the drives to be connected to a unit exceeds 2 Terabytes (TB), you can enable auto-carving when you configure your units. www.3ware.com 13