RE: linux DBA's: O_Direct
- From: "Teehan, Mark" <mark.teehan@xxxxxxxx>
- To: "'kevinc@xxxxxxxxxxxxx'" <kevinc@xxxxxxxxxxxxx>, "Oracle-L" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 23 Nov 2005 14:16:34 +0800
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@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]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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