Direct I/O does not enhance raw I/O performance. Raw I/O performance is
still slightly faster than direct I/O, but if you want the benefits of a JFS
and enhanced performance, direct I/O is highly recommended


Summary
Direct I/O requires substantially fewer CPU cycles than regular I/O.
I/O-intensive applications that do not get much benefit from the caching
provided by regular I/O can enhance performance by using direct I/O. The
benefits of direct I/O will grow in the future as increases in CPU speeds
continue to outpace increases in memory speeds.

What types of programs are good candidates for direct I/O? Programs that are
typically CPU-limited and perform lots of disk I/O. "Technical" codes that
have large sequential I/Os are good candidates. Applications that do
numerous small I/Os will typically see less performance benefit, because
direct I/O cannot do read ahead or write behind. Applications that have
benefited from striping are also good candidates.


This is on the web .

Balanand Pinni

-----Original Message-----
From: Paul Ripke [mailto:stixpjr AT BIGPOND.NET DOT AU]
Sent: Thursday, April 24, 2003 10:08 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: AIX and async I/O

On Thursday, Apr 24, 2003, at 19:07 Australia/Sydney, Wilcox, Andy
wrote:

> Thanks for all of your thoughts so far.... I am aware of the async I/O
> requirements for Oracle, but never played with direct I/O. I will do
> some
> testing with this and see what I can find out, and post some any
> findings
> here for your reference.

I haven't got the PDFs handy, but I have a vague recollection that
direct I/O is enabled by default in the 5.1 server on AIX...

It should provide almost all the advantages of using raw volumes, and
IMHO, for TSM DB, log and stgpool volumes, is an excellent idea. I
wonder
if/when Oracle is going to support this?

Cheers,
--
Paul Ripke
Unix/OpenVMS/TSM/DBA
101 reasons why you can't find your Sysadmin:
68: It's 9AM. He/She is not working that late.
-- Koos van den Hout