IBM 86624RY Maintenance Manual - Page 97

Disable or Enable Read-Ahead Cache Mode: These choices are available in the Information mode only. When read-ahead cache is set to Enabled (default setting), the ServeRAID controller transfers data from a disk to its local cache in increments equal to the stripe-unit size. This provides excellent overall performance when workloads are steady and sequential. However, if the workload is random or the system I/O requests are smaller than the stripe-unit size, reading ahead to the end of the stripe might degrade performance. When read-ahead cache is set to Disabled, the ServeRAID controller transfers data from a disk to local cache in increments equal to the system I/O request size, without reading ahead to the end of the stripe. Change the Rebuild Rate: This choice is available in the Information mode only. You can select this choice to set the priority for Rebuild operations to High (default), Medium, or Low. - When the rebuild rate is set to High, the rebuild I/O request gets high priority in the execution order. - When the rebuild request is set from High to Medium in a heavily loaded system, it can increase the rebuild time, but provide better system performance. - When the rebuild request is set from High or Medium to Low in a moderate to heavily loaded system, it can increase the disk rebuild time, but provide better system performance. Change the Stripe-Unit Size: This choice is available in the Information mode only. Attention After you configure an array and store data on the logical drives, you cannot change the stripe-unit size without destroying data in the logical drives. The stripe-unit size is the amount of data written on a given disk before writing on the next disk. To maximize the overall performance, choose a size Netfinity 5500 M20 - Type 8662 89