Evaluating Performance Impact - HP Surestore Disk Array 12h - And FC60 Service Manual

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
RAID level
Setting:
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
of each RAID level.
Stripe segment size
Setting:
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 read-
modify-write). Small segment sizes are typically useful for applications that require large
numbers of small I/Os to be processed quickly.
Managing Disk Array Capacity
196
for more information on the performance characteristics