HSG80 ACS Solution Software V8.6 for IBM AIM Installation and Configuration Guide

Planning Storage 2–27
Large chunk sizes also tend to increase the performance of random reads and writes. It is
recommended that you use a chunk size of 10 to 20 times the average request size,
rounded to the closest prime number.
To calculate the chunk size that should be used for your subsystem, you must first analyze
the types of requests that are being made to the subsystem:
■ Many parallel I/Os that use a small area of disk should use a chunk size of 10 times the
average transfer request rate.
■ Random I/Os that are scattered over all the areas of the disks should use a chunk size
of 20 times the average transfer request rate.
■ If you do not know, then you should use a chunk size of 15 times the average transfer
request rate.
■ If you have mostly sequential reads or writes (like those needed to work with large
graphic files), make the chunk size for RAID 0 and RAID 0+1 a small number (for
example: 67 sectors). For RAID 5, make the chunk size a relatively large number (for
example: 253 sectors).
Table 2–2 shows a few examples of chunk size selection.
e
Increasing Sequential Data Transfer Performance
RAID 0 and RAID 0+1 sets intended for high data transfer rates should use a relatively
low chunk size (for example: 67 sectors). RAID 5 sets intended for high data rate
performance should use a relatively large number (for example: 253 sectors).
Table 2–2 Example Chunk Sizes
Transfer Size (KB) Small Area of I/O Transfers Unknown Random Areas of I/O Transfers
241 5979
4 79 113 163
8 157 239 317