IBM 86605SU Maintenance Manual - Page 86

Understanding Disk Array Technology When you connect several hard disks together and configure the RAID controller to access them in a predetermined pattern, you create a disk array. The ServeRAID controller on your system board supports up to eight independent arrays. Disk arrays are used to improve security, performance, and reliability. The amount of improvement depends on the application programs that you run on the server and the RAID levels that you assign to the logical drives in your arrays. The ServeRAID controller supports RAID levels 0, 1, and 5. Your server has space for up to six hot-swap hard disk drives. Hard Disk Drive Capacities: Hard disk drive capacities influence the way you create arrays. Drives in the array can be of different capacities (1 GB1 or 2 GB, for example), but the ServeRAID controller treats them as if they all have the capacity of the smallest disk drive. For example, if you group three 1 GB drives and one 2 GB drive into an array, the total capacity of the array is 1 GB times 4, or 4 GB, not the 5 GB physically available. Conversely, if you add a smaller drive to an array of larger drives, such as a 1 GB drive to a group containing three 2 GB drives, the total capacity of that array is 4 GB, not the 7 GB physically available. Therefore, the optimal way to create arrays is to use hard disk drives that have the same capacity. Logical Drives: When you create an array, you group hard disk drives into one storage area. You can define this storage area as a single logical drive, or you can subdivide it into several logical drives. Each logical drive appears to the operating system as a single physical hard disk drive. The ServeRAID controller on your system board supports up to eight logical drives. If you have only one array, you can define it as a single logical drive, or you can divide it into several logical drives. The first logical drive that you define will be your startup (boot) drive. If you have two or more arrays, each array can be one logical drive, or you can divide each array into multiple logical drives, as long as the total number of logical drives for all of the arrays does not exceed eight. 1 When referring to hard-disk-drive capacity, GB means 1 000 000 000 bytes; total user-accessible capacity may vary depending on operating environment. Netfinity 5500 - Type 8660 81