HP StorageWorks HSG80 ACS Solution Software V8.8 for Windows NT, Windows 2000, and Windows Server 2003 (32-bit) Installation and Configuration Guide (AA-RV1XA-TE, March 2005)

Planning Storage Configurations
92 HSG80 ACS Solution Software V8.8 for Windows NT, Windows 2000, and Windows Server
2003 (32-bit) Installation and Configuration Guide
■ CHUNKSIZE=DEFAULT lets the controller set the chunk size based on the
number of disk drives (d) in a stripeset or RAIDset. If number of drives is less
or equal to 9, then chunk size = 256. If the number of drives is greater than 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, separate I/O requests can be handled
in parallel, which increases the request rate. This concept is shown in Figure 32.
Figure 32: Large chunk size increases request rate
Large chunk sizes also tend to increase the performance of random reads and
writes. HP recommends 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:
CXO-5135A-MC
Chunk size = 128k (256 blocks)
Request A
Request B
Request C
Request D