|  |
|
Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 3:
SCSI Tuning Under AIX
# chdev -l
hdisk8 -a q_type=simple -a queue_depth=24
If
the disk array is attached via a SCSI-2 Fast/Wide SCSI adapter bus,
it may also be necessary to change the outstanding-request limit for
that bus. Let's look at that next.
The
AIX SCSI-2 Fast/Wide Adapter supports two SCSI buses; one for
internal devices and one for external devices. There is a limit on
the total number of outstanding requests that can be defined for
each bus. The default value of that limit is 40 for each bus and
the maximum is 128. When an IBM disk array is attached to a SCSI-2
Fast/Wide Adapter bus, the outstanding-request limit for the bus is
increased automatically to accommodate the queue depth of the disk
array. However, for a non-IBM disk array, this change must be
performed manually. For example, using chdev to set the
outstanding-request limit of adapter scsi2 to 80, you would
use:
# chdev -l
scsi2 -a num_cmd_elems=80
Note,
if you are using the SCSI-2 High Performance Controller, the maximum
number of queued requests is 30 and that limit cannot be changed.
For that reason, you should ensure the sum of the queue depths of
the devices attached to a SCSI-2 High Performance Controller does
not exceed 30.
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
Databases
ISBN
0-9745993-4-4
by Mike Ault
Oracle Consulting
Services
Burleson
Oracle Consulting offers Senior Oracle consultants which are available for all
areas of Oracle support. Common Oracle consulting support activities include
short-term Oracle tuning, Oracle database troubleshooting, Oracle9i and
Oracle10g migration,
Oracle9iAS App Server
consulting, Oracle design reviews and
Oracle requirements evaluation support. Oracle support and Oracle consulting
services are priced by the hour, so you only pay for what you need. These
one-time Oracle consulting services commonly include:
-
Answering
questions from your Oracle DBA technical staff
-
Repairing down
production Oracle database systems
-
One-time
Oracle tuning evaluation
-
Guru support
for your Oracle DBA
-
Installation
of Oracle application packages
For more
information, please visit
www.rampant-books.com
|
