IBM 86655RY Hardware Maintenance Manual - Page 203

Stripe-unit size With RAID technology, data is striped across an array of physical drives. This datadistribution scheme complements the way the operating system requests data. The granularity at which data is stored on one drive of the array before subsequent data is stored on the next drive of the array is called the stripe-unit size. You can control the stripe-unit size and maximize the performance of your ServeRAID controller by setting a stripe-unit size to a value that is close to the size of the system I/O requests. You can set the stripe-unit size to 8 KB, 16 KB, 32 KB, or 64 KB. For example, performance in transaction-based environments, which typically involve large blocks of data, might be optimal when the stripe-unit size is set to 32 KB or 64 KB. However, performance in file and print environments, which typically involve multiple small blocks of data, might be optimal when the stripe-unit size is set to 8 KB or 16 KB. The collection of stripe units, from the first drive of the array to the last drive of the array, is called a stripe. Supported RAID levels Disk arrays are used to improve 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. The ServeRAID controllers support RAID level-0, 1, 1E, 5, 5E, 00, 10, 1E0, and 50. Understanding RAID level-0: RAID level-0 stripes the data across all the drives in the array. This offers substantial speed enhancement, but provides no data redundancy. RAID level-0 provides the largest storage capacity of the RAID levels that are offered, because no room is taken for redundant data or data-parity storage. RAID level-0 requires a minimum of one drive and supports a maximum of 16 drives. The following illustration shows an example of a RAID level-0 logical drive. Start with two physical drives. Installing and configuring ServeRAID controllers 193