HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning Storage Configurations
2–31HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
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Figure 2–13: Large chunk size increases request rate
Large chunk sizes also tend to increase the performance of random reads and writes.
StorageWorks 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:
• 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).
CXO-5135A-MC
Chunk size = 128k (256 blocks)
Request A
Request B
Request C
Request D