Re: DBWR, Direct I/O and the Devil

From: Greg Rahn <greg_at_structureddata.org>
Date: Thu, 29 Nov 2007 09:59:36 -0800
Message-ID: <a9c093440711290959o7c46270bxe103bc15775f98d7@mail.gmail.com>

On 11/28/07, Don Seiler <don_at_seiler.us> wrote:
> Alright so I should set filesystemio_options=setall rather than
> directio? Are there any other parameters to look at?

It's best to set
filesystemio_options=directio
because your filesystem does not support async io. (Perhaps a reason to use ASM?)

> Don't I still need to mount the disk with "mincache=direct,convosync=direct"?

This shouldn't matter. With the filesystemio_options=directio the oracle files should be opened with the O_DIRECT flag but those mount options force it for *all* files, not just oracle ones. Net net, its the same for oracle files.

> My connotation was that direct I/O the opposite of asynchronous I/O.
> I'm seeing now that they are more or less independent states of I/O
> covering different aspects of behavior.

Buffered and direct I/O (unbuffered) are opposites. Asynchronous and synchronous are opposites. Two different attributes, two different options. Generally direct/async is best. This is what raw and ASM use, as well as vxfs with ODM or QickIO.

-- 
Regards,

Greg Rahn
http://structureddata.org
--
http://www.freelists.org/webpage/oracle-l

Received on Thu Nov 29 2007 - 11:59:36 CST