Re: DBWR, Direct I/O and the Devil

On 11/28/07, Don Seiler <don@xxxxxxxxx> 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

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