RAID Array 410 HSZ40 HSOF Software Version 3.7 for Compaq Tru64 UNIX Release Notes

RAID Array 410 HSZ40 HSOF Software Version 3.7 for Compaq Tru64 UNIX
Page 40 AA–RMBXA − TE
CAUTION
The default chunk size should be used with caution. It is
imperative that you analyze the I/O transfers being used
with your application to determine the proper chunk
size. An improper value used as a chunk size may cause
serious performance problems with the subsystem.
• 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.
8.1.1.2
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 8–1.
Figure 8-1 Chunk Size Larger than the Request Size
CXO-5135A-MC
Chunk size = 128k (256 blocks)
Request A
Request B
Request C
Request D
Applications such as interactive transaction processing, office automation, and
file services for general timesharing tend to require high I/O request rates.