HP Surestore Disk Array FC60 HP SureStore E Disk Array FC60 Service Manual (A5 - Page 196

Evaluating Performance Impact Several disk array configuration settings have a direct impact on I/O performance of the array. When selecting a setting, you should understand how it may affect performance. Table 23 identifies the settings that impact disk array performance and what the impact is. Table 23 Performance Impact of Configuration Settings Setting: RAID level Function: Sets the RAID level used by the volume group. Performance Impact: The RAID level selected impacts the entire performance profile for the volume group. Read I/O and write I/O performance are directly influenced by the RAID level. See "RAID Level Comparisons" on page 55 for more information on the performance characteristics of each RAID level. Setting: Stripe segment size Function: Sets the number of blocks of data the controller will write to or read from a single disk before switching to the next disk in the volume. Performance Impact: Optimum performance is typically achieved when the segment size matches the I/O size. In this case, only one disk is required to service an I/O, leaving the remaining disk in the volume available for other I/Os. A large segment size provides good read performance in most RAID levels. The controller will have to access fewer disks to retrieve the data, leaving the remaining drives available for other I/O operations. Large segment sizes are typically useful for applications that require high I/O throughput. A small logical unit segment size is useful for most RAID 5 write applications, because the controller firmware is capable of performing group writes (writing of data simultaneously to multiple disks, while calculating the parity for the stripe, as opposed to the single-threaded readmodify-write). Small segment sizes are typically useful for applications that require large numbers of small I/Os to be processed quickly. 196 Managing Disk Array Capacity