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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