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

2–26 HSG80 ACS Solution Software Version 8.6 for IBM AIX Installation and Configuration Guide
Chunk Size
Specify the chunk size of the data to be stored to control the stripesize used in RAIDsets
and stripesets:
■ CHUNKSIZE=DEFAULT lets the controller set the chunk size based on the number of
disk drives (d) in a stripeset or RAIDset. If d ≤ 9 then chunk size = 256. If d > 9 then
chunk size = 128.
■ CHUNKSIZE=n lets you specify a chunk size in blocks. The relationship between
chunk size and request size determines whether striping increases the request rate or
the data-transfer rate.
Increasing the Request Rate
A large chunk size (relative to the average request size) increases the request rate by
enabling multiple disk drives to respond to multiple requests. If one disk drive contains all
of the data for one request, then the other disk drives in the storageset are available to
handle other requests. Thus, in principle, separate I/O requests can be handled in parallel,
thereby increasing the request rate. This concept is shown in Figure 2–18.
Figure 2–18. Chunk size larger than the request size
CXO-5135A-MC
Chunk size = 128k (256 blocks)
Request A
Request B
Request C
Request D