HP Surestore Disk Array FC60 Disk Array FC60 User's Guide (A5635A) - Page 122

Setting, Function, Performance Impact

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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 43 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. 122

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122
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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 43
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 read-
modify-write). Small segment sizes are typically useful for applications that require large
numbers of small I/Os to be processed quickly.