Understanding RAID Concepts and Levelswww.3ware.com 11Through 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), and rounded downto the nearest 5 GBytes for drives over 45 GB. For example, a 44.3 GB drivewill 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 drivecoercion under “Creating a Hot Spare” on page 139.Support for Over 2 TerabytesWindows 2000, Windows XP, Linux 2.4, and FreeBSD 4.x, do not currentlyrecognize unit capacity in excess of 2 TB.If the combined capacity of the drives to be connected to a unit exceeds 2Terabytes (TB), you can enable auto-carving when you configure your units.Auto-carving divides the available unit capacity into multiple chunks of 2 TBor smaller that can be addressed by the operating systems as separatevolumes. The carve size is adjustable from 1024 MB to 2048 MB (default)prior to unit creation.If a unit over 2 TB was created prior to enabling the auto-carve option, itscapacity visible to the operating system will still be 2TB; no additionalcapacity will be registered. To change this, the unit has to be recreated.For more information, see “Using Auto-Carving for Multi LUN Support” onpage 121.RAID 50 (number of drives - number of groups of drives) X (capacity of thesmallest drive)Table 4: Drive CapacityRAID Level Capacity
