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From: Bruce on 11 Mar 2010 01:55
Hi All,

I note that using direct I/O (by setting the forcedirectio while
mounting the database file systems) and bypassing the file system
cache may improve database performance significantly, but this should
be done only for file systems in which database files and redo log
files exist. If direct I/O is used and there is not enough database
buffer cache, it may even decrease the performance by moving the
problem from double buffering to a lack of database buffer cache. So,
this performance tuning must be planned carefully, and the database
buffer cache should be sized properly. The direct I/O option should
not be used for other file systems used by other applications because
they still need the UFS buffer cache.

Now, I have Oracle database installed inside a non-global zone and I
see a lot of Asynchronous I/O wait warnings in the Oracle Alert log
file. Storage mount points with UFS filesystem contain the Oracle
datafiles and redo log files. In addition, two Oracle datafiles of 10
GB each reside on the local disks. The Oracle init.ora parameter to
set asynchronous I/O for Oracle database files is
FILESYSTEMIO_OPTIONS= SETALL.

Although the above parameter was set during the database installation,
the aiowait warnings don't seem to disappear.

Can I use the "forcedirectio" option at the Operating System /etc/
vfstab file for Oracle datafiles and redo log files?

Or, should I just move the Oracle database files residing on the local
disks to the external storage? Will this take care of aiowait warnings
and if yes, how? The storage is a DAS.

Regards,
Bruce
From: joel garry on 11 Mar 2010 11:49
On Mar 10, 10:55 pm, Bruce <brucemcgill....(a)gmail.com> wrote:
> Hi All,
>
> I note that using direct I/O (by setting the forcedirectio while
> mounting the database file systems) and bypassing the file system
> cache may improve database performance significantly, but this should
> be done only for file systems in which database files and redo log
> files exist. If direct I/O is used and there is not enough database
> buffer cache, it may even decrease the performance by moving the
> problem from double buffering to a lack of database buffer cache. So,
> this performance tuning must be planned carefully, and the database
> buffer cache should be sized properly. The direct I/O option should
> not be used for other file systems used by other applications because
> they still need the UFS buffer cache.
>
> Now, I have Oracle database installed inside a non-global zone and I
> see a lot of Asynchronous I/O wait warnings in the Oracle Alert log
> file. Storage mount points with UFS filesystem contain the Oracle
> datafiles and redo log files. In addition, two Oracle datafiles of 10
> GB each reside on the local disks. The Oracle init.ora parameter to
> set asynchronous I/O for Oracle database files is
> FILESYSTEMIO_OPTIONS= SETALL.
>
> Although the above parameter was set during the database installation,
> the aiowait warnings don't seem to disappear.
>
> Can I use the "forcedirectio" option at the Operating System /etc/
> vfstab file for Oracle datafiles and redo log files?
>
> Or, should I just move the Oracle database files residing on the local
> disks to the external storage? Will this take care of aiowait warnings
> and if yes, how? The storage is a DAS.
>
> Regards,
> Bruce

There are a bunch of MOS notes on solaris setall, including one about
a mandatory patch. It varies by Oracle version/patch level, which I
can't seem to find in your post. Start with How To Verify Whether
DIRECTIO is Being Used [ID 555601.1]

jg
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