Re: some one has experiece using direc io in nt, not using raw disks
- From: Vladimir Begun <vladimir.begun@xxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 05 Jul 2004 17:15:27 -0700
Juan Carlos Reyes Pacheco wrote:
> Oracle Performance Tuning Oracle course says
> "On some operating systems, such as Windows NT, Oracle Server process does
> not use o/s file system cache i/o operations. In this cases, use of raw
> devices may not show significant performance gains"
I.e. Oracle does use Direct I/O by default even on cooked file systems,
as it's written in the documentation (please see that quotation I posted).
> I found a test, and there was some improvement using raw files.
I think it's all about words 'may not', 'significant', 'some' -- would you
please publish the link to that test? See a quotation at the end of my
message, probably, it would shed some more light.
> As I understand what you say is
That time I did not say anything :) I did cut&paste some information from
official Oracle documentation.
> it is a good idea to use direct io in NT, without raw files.?
Oracle does use Direct I/O by default even on cooked file systems and
as far as I know you do not have any option to switch it off; I'm not
Windows expert though.
Please check this as well:
http://www.ixora.com.au/q+a/io.htm
"Oracle on NT always explicitly does direct I/O. The datafiles are
created and opened with FILE_FLAG_NO_BUFFERING and thus IRP_NOCACHE
is always set. This means that there is no requirement on NT to
match the database block size to the underlying operating system
block sizes, as is the case on Unix. The down-side is that using
direct I/O disables NT's fast I/O path, which means that the I/O
request packets have to be hand-passed all the way down through the
all the kernel layers and back up again, which even the Microsoft
people regard as grossly inefficient. Because of this overhead, you
should actually use a larger block size on NT than you might otherwise
have done on Unix, so that you can get as much data for each I/O
operation as possible."
So, your questions about "direct I/O experience people have" can
be answered like -- yes, all of them have such experience.
--
Vladimir Begun
The statements and opinions expressed here are my own and
do not necessarily represent those of Oracle Corporation.
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