HP 273914-B21 Smart Array 6400 Series Controllers User Guide - Page 30

30 HP Smart Array 6400 Series Controllers User Guide Accelerator ratio The controller has an onboard cache called an Array Accelerator, which performs both write-posting and read-ahead caching. The setting in CPQONLIN determines the amount of memory allocated to the read and write caches. For example, if the accelerator ratio is set to Read 75%:Write 25%, 75% of Array Accelerator cache is dedicated to read-ahead cache and 25% is dedicated to the write-posting cache. This option can be modified from the Controller Settings menu. Expanding an array During an expand, performance may be slightly degraded. In most cases, however, any potential degradation is offset by the addition of physical drives. Some tips for expanding include: • Perform the expand process during periods of low server use. If you must expand during peak periods, CPQONLIN enables you to set the priority of the expand. Setting the priority to LOW affects performance the least, but it takes longer for the new space to become available. • When expanding, always add drives with a capacity equal to or greater than the capacity of the smallest drive in the array. Adding larger drives wastes space because only the space that is equal to the smallest drive size can be used. Adding or configuring spare drives When adding a spare drive to an array, an unassigned drive must exist or a drive already assigned as a spare must exist on another array. You can assign a single spare to any number of arrays or assign separate spares. When you select Assign Spare Drive, only drives that qualify appear (for example, only those spares that are large enough appear). If drives that you expect to see do not appear, switch to the physical drive view (Tab key), and check the size of the drives. The capacity of the spare must be equal to or greater than the capacity of the smallest drive in the array.