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

Planning Storage Configurations
2–30 HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
• Destroy/Nodestroy
•Geometry
Each of these switches is described in the following sections.
NOTE: After initializing the storageset or disk drive, you cannot change these switches without
reinitializing the storageset or disk drive.
Chunk Size
With ACS software, a parameter for chunk size (chunksize=default or n) on some
storagesets can be set. However, unit performance may be negatively impacted if a
non-default value is selected as the chunksize.
If a non-default chunk size has been calculated, verify that the chunk size value is
divisible by 8, with no remainder. If the value is not aligned with this rule, adjust the
chunk size value upward until it divisible by 8, with no remainder.
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 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 2–13.