On 25/07/16 14:51, Christine Caulfield wrote: > On 25/07/16 14:29, Thomas Lamprecht wrote: >> Hi all, >> >> I'm currently testing the new features of corosync 2.4, especially >> qdevices. >> First tests show quite nice results, like having quorum on a single node >> left out of a three node cluster. >> >> But what I'm a bit worrying about is what happens if the server where >> qnetd runs, or the qdevice daemon fails, >> in this case the cluster cannot afford any other loss of a node in my >> three node setup as votes expected are >> 5 and thus 3 are needed for quorum, which I cannot fulfill if the qnetd >> does not run run or failed. > > We're looking into ways of making this more resilient. It might be > possible to cluster a qnetd (though this is not currently supported) in > a separate cluster from the arbitrated one, obviously. > > The LMS algorithm is quite smart about how it doles out its vote and can > handle isolation from the main qnetd provided that the main core of the > cluster (the majority in a split) retains quorum, but any more serious > changes to the cluster config will cause it to be withdrawn. So in this > case you should find that your 3 node cluster will continue to work in > the absence of the qnetd server or link, provided you don't lose any nodes. >
I should have also said that you'll need to enable 'wait_for_all' for this to work. Chrissie > In a 3 node setup obviously LMS is more appropriate than ffsplit anyway. > > Chrissie > >> >> So in this case I'm bound to the reliability of the server providing the >> qnetd service, >> if it fails I cannot afford to loose any other node in my three node >> example, >> or also in any other example with uneven node count as the qdevice vote >> subsystems provides node count -1 votes. >> >> So if I see it correctly QDevices make only sense in case of even node >> counts, >> maybe especially 2 node setups as if qnetd works we have on more node >> which may fail and if qnetd failed >> we are as good as without it as qnted provides only one vote here. >> >> Am I missing something, or any thoughts to that? >> >> >> >> _______________________________________________ >> Users mailing list: [email protected] >> http://clusterlabs.org/mailman/listinfo/users >> >> Project Home: http://www.clusterlabs.org >> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf >> Bugs: http://bugs.clusterlabs.org > > > _______________________________________________ > Users mailing list: [email protected] > http://clusterlabs.org/mailman/listinfo/users > > Project Home: http://www.clusterlabs.org > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > Bugs: http://bugs.clusterlabs.org > _______________________________________________ Users mailing list: [email protected] http://clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org
