linux DBA's: O

From: Teehan, Mark <mark.teehan_at_csfb.com>
Date: Tue, 22 Nov 2005 11:36:31 +0800
Message-ID: <7EED3949F5157540B4B5307A7E9857040EB2C9@esng11p32002.csfb.cs-group.com>

Redhat 3 ES, 2.4.21-32.0.1.ELsmp, Oracle 10.2.0.1 RAC, OCFS 1.0.12

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 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.

I want to use direct_io for backups so that there is no filesystem caching. If have set filesystemio_options=directIO, ext3 doesnt like it at all - rman is unable to write the file header after attempting to open it with O_DIRECT. I have tried mounting the system system with the "sync" option but this doesnt help.

Are other linux DBA's seeing the same problem and has anybody succeeded in getting direct IO working on ext3? Ultimately I dont want any filesystem block caching at all: let it behave like solaris. OS upgrades are not an option as it is supposed to be working no these versions of everything.

Any help appreciated.

Mark

Please access the attached hyperlink for an important electronic communications disclaimer:

http://www.csfb.com/legal_terms/disclaimer_external_email.shtml

--
http://www.freelists.org/webpage/oracle-l

Received on Mon Nov 21 2005 - 21:38:53 CST

linux DBA's: O_Direct