RE: active-pasive cluster in linux
Date: Tue, 23 Feb 2010 13:08:21 -0500
Message-ID: <8DE2E2D2D62A44E3BF0EF93CF5C980F1_at_rsiz.com>
Most ports support a read only mount of a volume mounted read/write on one node. The only wrinkle I've noticed is that the appearance of new objects on the non-rw node may be slightly delayed. I'm uncertain of the exact mechanism of this delay, and it may vary by port.
An interesting application of this is mounting all the log directories (both archived redo and diagnostic) as read only without the need for clustering software at the file system level. (They still have to be shareable volumes, of course). IF you're not storing online redo in ASM this can also be used for the online redo logs, but of course you need the dbfiles multi-rw-able for any flavor of RAC. But this thread isn't really about RAC.
Purely for the active-passive idea, this of course means you can tail files on read mounted volumes and see the dying diagnostics from a crashed node without waiting for some other node to start or waiting to mount the volumes. Then you have the last messages at hand if you want to look at them before you activate the passive node. This can save a lot of time if the logs are telling you about, for example, media failure or some other issue that will just be repeated on the passive node.
Presumably the interest in this type of architecture is minimizing the time until the applications are available on the passive node if the active node is in some sort of failure, as well as for routine planned switchover for preventive maintenance and just to prove it will work.
<I wrote too much. I just wanted to introduce the notion about non-corrupting read only mountablility even without a clustered file system; David is absolutely correct you don't want multiple concurrent rw mounts without a clustered file system, even if you can trick the OS into doing it for you.>
mwf
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of David Ballester
Sent: Monday, February 22, 2010 6:26 PM
To: LS Cheng
Cc: jcmiranda_at_oesia.com; oracle-l_at_freelists.org
Subject: Re: active-pasive cluster in linux
2010/2/22 LS Cheng <exriscer_at_gmail.com>
Hi
You can use OCFS2 if you wish but basically you need some sort of Cluster Filesystem or Volume Manager such as ASM.
I dont mention OCFS2 because introducing two clustering software (OCFS2 and CRS) for a Single instance Active Passive solution is a bit too much in my opinion that is why I said you are forced to use ASM (runs on top of CRS).
Thanks
Or not use ocfs2 or any cluster filesystem, the only node that needs to have mounted the filesystems is the active one
If you try to mount a non cluster filesystem in another node while is mounted in a first one, the other node should answer 'partition used' or something similar ( prevents corruption )
when switching from nodes, as part of the automatic process, one node should umount and the other mount ( may be fsck first )
Regards
D.
-- http://www.freelists.org/webpage/oracle-lReceived on Tue Feb 23 2010 - 12:08:21 CST