On Fri, Nov 25, 2011 at 7:05 AM, Hellemans Dirk D <dirk.hellem...@hpcds.com> wrote: > Hello everyone, > > > > I’ve been reading a lot lately about using Corosync/Openais in combination > with Pacemaker: SuSe Linux documentation, Pacemaker & Linux-ha website, > interesting blogs, mailinglists, etc. As I’m particularly interested in how > well two node clusters (located within the same server room) are handled, I > was a bit confused by the fact that quorum disks/ quorum servers are (not > yet?) supported/used. Some suggested to add a third node which is not > actively participating (e.g. only running corosync.... or with hearbeat but > in standby mode). That might be a solution but doesn’t “feel” right, > especially if you consider multiple two-node clusters... that would require > a lot of extra “quorum only nodes”. Somehow SBD (storage based death) in > combination with a hardware watchdog timer seemed to also provide a > solution: run it on top of iSCSI storage and you end up with a fencing > device and some sort of “network based quorum” as tiebreaker. If one node > loses network connectivity, sbd + watchdog will make sure it’s being fenced. > > > > I’d love to hear your ideas about 2 node cluster setups. What is the best > way to do it? Any chance we’ll get quorum disks/ quorum servers in the > (near) future? > > > > In addition, say you’re not using sbd but an IPMI based fencing solution. > You lose network connectivity on one of the nodes (I know, they’re redundant > but still...sh*t happens ;) Does Pacemaker know which of both nodes lost > network connectivity? E.g.: node 1 runs Oracle database, node 2 nothing. > Node 2 loses network connectivity (e.g. both NICs without signal because > unplugged by an errant technician ;) )... => split brain situation occurs, > but who’ll be fenced? The one with Oracle running ?? I really hope not... > cause in this case, the cluster can “see” there’s no signal on the NICs of > node2. Would be interesting to know more about how Pacemaker/corosync makes > such kind of decisions... how to choose which one will be fenced in case of > split brain. Is it randomly chosen? Is it the DC which decides? Based on NIC > state? I did some quick testing with 2 VMs and at first, it looks like > Pacemaker/corosync always fences the correct node, or: the node where I > unplugged the “virtual” cable. > > > > I’m curious! > > > > Thanks a lot! > > > > Best regards, > > Dirk > > _______________________________________________ > Pacemaker mailing list: Pacemaker@oss.clusterlabs.org > http://oss.clusterlabs.org/mailman/listinfo/pacemaker > > Project Home: http://www.clusterlabs.org > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > Bugs: http://bugs.clusterlabs.org > >
Hello Hellemans, I can't speak much for the lack of quorum support outside of a 2 node cluster, other than you can get additioanl support using cman. I personally don't like adding another partial cluster stack into the equations. And I don't think Suse Enterprise supports the RH technology. As for node fencing order, this can always be manipulated through the use of: * Resource stickiness * Location/collocation/anti-location You could also using the network RAs (IPAddr2, and ping), to determine node network connectivity, and *order* the way your configuration starts-up. Cheers, Nick. _______________________________________________ Pacemaker mailing list: Pacemaker@oss.clusterlabs.org http://oss.clusterlabs.org/mailman/listinfo/pacemaker Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org
