Specifications

4–44 Planning Storagesets
Increasing the Request Rate
A large chunk size (relative to the average request size) increases the request rate by
allowing 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 4–13.
Figure 4–13. Chunk Size Larger than the Request Size
Applications such as interactive transaction processing, office automation, and file
services for general timesharing tend to require high I/O request rates.
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 up to the nearest multiple of 64. In general, a chunk size of 256 works
well for UNIX® systems; 128 works well for OpenVMS™ systems.
CXO-5135A-MC
Chunk size = 128k (256 blocks)
Request A
Request B
Request C
Request D