Laurent,
I never used DRDB (We have a SAN here...), or heartbeat either, but I suspect
you will need to configure the OCFS2 timeouts to be larger than the heartbeat2
timeouts so that DRDB can resolve itself before the OCFS2 causes the machine to
fence.
Also you probably will want to configure the heartbeat2 to use a third machine
(try to ping a router for example) to decide which server to keep alive. When
using Oracle the CRS stack uses the ethernet interface status to decide.
Regards,
Luis
Laurent Neiger <Laurent.Neiger@grenoble.cnrs.fr> wrote: Hi all,
We're building a 2-node cluster that we'd like to work in active/active
mode.
Since drbd 8.x this feature is possible so we hope to achieve a cluster
where
the 2 nodes would be able to share the load, not only one and the other node
in stanby mode, waiting for the primary's failure...
In order to have a drbd active/active mode, we need to have a cluster
filesystem,
handling DLM. Our choice went to OCFS-2 for its numerous features.
But we encountered a problem : when we cut off the network link of,
let's say
node2, for simulating a crash, we managed to make node 1 fence node2 via
drbd
in order to avoid a split-brain configuration, but node1 then self-fence
itself
apparently due to ocfs2.
After some researches, we understood this seems to be a "normal"
feature :
in a 2-node cluster, when communication (and so ocfs2 heartbeat) is lost,
the remaining node has no way to know if it's its peer which is down or
itself which is away from the cluster, so it self-fences.
Our first idea was so to add a third node, so that the 2 remainning nodes
still communicate and no ocfs2 self-fence is launched.
But ocfs2 heartbeat, as explained in the FAQ, writes to the heartbeat
system file,
which has to be shared. If we set up a third node with a little ocfs2
partition
and o2cb, it doesn't appear into the cluster, even when declared as
third node
in /etc/ocfs2/cluster.conf (of each node). Because the ocfs2 partition
on the
third node is not shared, so ocfs2 heartbeat is not shared.
If we run ocfs2_hb_ctl -I -d /dev/drbd0 on node0 and node1, we get back
the same reference for heartbeat, but a different one on node2 (third node).
And in /var/log/kern.log on node 0, we have
...
Feb 28 11:46:42 maq1 kernel: ocfs2_dlm: Node 1 joins domain
FB305B8298D94DCA9F9BF75D0AA09B8D
Feb 28 11:46:42 maq1 kernel: ocfs2_dlm: Nodes in domain
("FB305B8298D94DCA9F9BF75D0AA09B8D"): 0 1
But nothing about node2...
And we cannot share a common partition as drbd only works with 2 peers...
Would anyone have any hint about how we could solve this issue ?
Is there a way to make a 2-node ocfs2 cluster work
or must we have at least 3 nodes ?
But if 3 nodes are required, how to make it work with DRBD ?
Or in 2-node config., can we block self-fencing (but is it desirable) ?
Many thanks in advance for your help,
Best regards,
Laurent.
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email;internet:Laurent.Neiger@grenoble.cnrs.fr
title;quoted-printable:Administrateur Syst=C3=A8mes & R=C3=A9seaux
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