Two node Pacemaker with one Corosync only quorum node
Brian Campbell <brian.campbell <at> editshare.com>
2014-09-02 23:29:39 GMT
I'm wondering if there are any problems that would occur if you ran a
cluster with only two nodes running Pacemaker, but add a third Corosync
only node to provide quorum.
I tried this setup, and it appears to work fine after some brief testing; I
configured Corosync and votequorum appropriately on all three nodes, but
only ever started Pacemaker on two of them. After enabling
no-quorum-policy=stop, if I disconnected one of the nodes it would stop
itself and the other would take over like I expect, rather than both nodes
trying to promote themselves as occurs when there are only two nodes and
no-quorum-policy=ignore (for the purposes of debugging and development, I
don't have stonith enabled in order to make it easier to monitor what's
going on at each node, without my connection dropping due to rebooting the
I'm now wondering if there will be any problems I haven't anticipated with
this setup, or anything I should look out for.
Of course, other options would involve having the third node simply running
Pacemaker but permanently in standby, or making it an asymmetric cluster
and only allowing any resources to run on the first two nodes. But I'm
curious if it's possible to go the simplest possible route and just have
corosync running on a third quorum node; or possibly even more.
Our setup has a couple of master nodes with large amounts of RAM so that
all of the metadata can fit into RAM, and then a number of cheap storage
nodes to store the actual bulk data. Because we have the cheap storage
nodes, we have a number of machines we can run as quorum-only nodes, but
don't want to ever accidentally select them as a master or slave node.