Hi Lon and Thanks for this reply. In fact, thinking about it, my test wasn't very much representative of what I was expecting to do.
I blocked the qdisk communications to only one node which, after reading your reply, kind of confirmed me that I did the wong test. I'm going to re run it by blocking all the nodes to the qdisk. I'll also try your ping tie-breaker. Brem 2009/8/13, Lon Hohberger <l...@redhat.com>: > > On Thu, 2009-08-13 at 00:45 +0200, brem belguebli wrote: > > > My understanding of qdisk is that it is used as a tie-breaker, but it > > looks like it is more a heatbeat vector than a simple tie-breaker. > > Right, it's a secondary membership algorithm. > > > > Until here, no real problem indeed, if the site gets apart from the > > other prod site and also from the third site (hosting the iscsi target > > qdisk) the 2 nodes from the failing site get evicted from the cluster. > > > > > > But, what if my third site gets isolated while the 2 prod ones are > > fine ? > > Qdisk votes will not be presented to CMAN any more, but the two sites > should remain online if they still have a "majority" of votes. > > > > The real question is what happens in case all the nodes loose access > > to the qdisk while they're still able to see each others ? > > Qdisk is just a vote like other voting mechanisms. If all nodes lose > access at the same time, it should behave like a node death. However, > the default action if _one_ node loses access is to kill that node (even > if CMAN still sees it). > > > > The 4 nodes have each 1 vote and the qdisk 1 vote. The expected quorum > > is 3. > > > > If I loose the qdisk, the number of votes falls to 4, the cluster is > > quorate (4>3) but it looks like everything goes bad, each node > > deactivate itself as it can't write its alive status (--> heartbeat > > vector) to the qdisk even if the network heartbeating is working > > fine. > > What happens specifically? Most of the actions qdiskd performs are > configurable. For example, if the nodes are rebooting, you can turn > that behavior off. > > > > I wrote a simple 'ping' tiebreaker based the behaviors in RHEL3. It > functions in many ways in the same manner as qdiskd with respect to vote > advertisement to CMAN, but without needing a disk - maybe you would find > it useful? > > http://people.redhat.com/lhh/qnet.tar.gz > > -- Lon > > -- > Linux-cluster mailing list > Linux-cluster@redhat.com > https://www.redhat.com/mailman/listinfo/linux-cluster >
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