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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 3:
SCSI Tuning Under AIX
fast-pathing
to specific points in the SMIT interface from the command line. The
fast path is smitty chgdsk to get the disk interface section
of SMIT. As an alternative, you can also use the chdev
command line command to change these parameters.
Let's
look at an example using chdev, if your system contained a
non-IBM SCSI disk drive hdisk7, the following command enables
queuing for that device and sets its queue depth to 3:
# chdev -l
hdisk7 -a q_type=simple -a queue_depth=3
That's fine for a single disk, but what about when you are dealing
with an entire non-IBM disk array? Let's look at that next.
Any
disk array appears to AIX as a single, rather large, disk drive. A
non-IBM disk array, like a non-IBM disk drive, will be of class
disk, subclass scsi, type osdisk (which is short
for "Other SCSI Disk Drive"). However, we know a disk array
actually contains a number of physical disk drives. Each
physical disk drive
can handle multiple requests, therefore the queue depth for the
disk array device has to be set to a value high enough to allow
efficient use of all of the physical devices. For example, if
hdisk8 were an eight-disk non-IBM disk array, where each disk
supports a queued depth of 3, an appropriate change using chdev
would be:
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
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