RE: linux DBA's: O_Direct

Kevin -

Setting filesystemio_options=Direct does indeed prompt rman to do a direct write, but ext3 on 2.4.21 doesnt like it and blows up. o_direct support on ext3 seems to be flaky. There seems to be no overall redhat setting that says "Dont buffer filesystem I/o. At all. Ever" and you have to screw around with filesystems to try and turn it off; I havent suceeded in doing this. Backing up to OCFS is not supported afaik. Tell me: what happens to your free memory when you are running a backup - or any large IO accross an ext3 filesystem (a tar or even a tape backup..)

Thanks
mark

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Kevin Closson Sent: 23 November 2005 13:57
To: Oracle-L
Subject: RE: linux DBA's: O_Direct

>>>>I run database backups to an ext3 filesystem, using both
>>>rman and regular hotbackups on different servers. Linux uses
>>>all available ram to cache the writes to ext3, which can

If this is RMAN, why isn't oracle using O_DIRECT for the ext3 target?

10gR2 will do open(,O_DIRECT,) on ext3 if you set filesystemio_options=directIO.
I would recommend doing that, but then I'd also recommend a filesystem where you can put any thing you please in there - without the worry of landmines to step on...none of this "Uh, I think I'll put some goodies in ocfs filesystem, but then I have to put these other goodies in ext3 so my system doesn't blow up"

Kevin Closson
Chief Architect, Database Solutions
PolyServe
www.polyserve.com

>>>reduce free memory to 10-20MB (the box has 12GB) - this is
>>>how it is supposed to work. Sometimes the kernel is unable
>>>to allocate ram for new processes when it drop to this level
>>>and causes errors. It seems to me that filesystem block
>>>caching is unsuitable for a database server - it is not an
>>>issue for OCFS, only for backups to ext3.
>>>>
>>>>[...]
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>>>>
>>>>
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