HSG80 ACS Solution Software V8.6 for SGI IRIX Installation and Configuration Guide

Planning Storage 2–27
■ 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).
Table 2–2 shows a few examples of chunk size selection.
e
Increasing Sequential Data Transfer Performance
RAID 0 and RAID 0+1 sets intended for high data transfer rates should use a relatively
low chunk size (for example: 67 sectors). RAID 5 sets intended for high data rate
performance should use a relatively large number (for example: 253 sectors).
Save Configuration
The SAVE CONFIGURATION switch is for a single-controller configuration only. This
switch reserves an area on each of the disks that constitutes the container being initialized.
The controller can write subsystem configuration data on this area. If the controller is
replaced, the new controller can read the subsystem configuration from the reserved areas
of disks.
If you specify SAVE_CONFIGURATION for a multi-device storageset, such as a stripeset,
the complete subsystem configuration is periodically written on each disk in the
storageset.
Table 2–2 Example Chunk Sizes
Transfer Size (KB) Small Area of I/O Transfers Unknown Random Areas of I/O Transfers
241 5979
4 79 113 163
8 157 239 317