Interesting read. Thank you for providing it! In this follow up post https://techthoughts.typepad.com/managing_computers/2007/10/more-about-quor.html the author mentions the following:
Ping tiebreaker Some HA systems provide a ping tiebreaker. To make this work, you pick a address outside the cluster to ping, and any partition that can ping that address has quorum. The obvious advantage is that it's very simple to set up - doesn't require any additional servers or shared disk. The disadvantage (and it's a big one) is that it's very possible for multiple partitions to think they have quorum. In the case of split-site (disaster recovery) type clusters, it's going to happen fairly often. If you can use this method for a single site in conjunction with fencing, then it will likely work out quite well. It's a lot better than no tiebreaker, or one that always says "you have quorum". Having said that, it's significantly inferior to any of the other methods. The quote "It's a lot better than no tiebreaker..." is what I am looking for. Is there something like a "ping tiebreaker" in the current world of pacemaker/corosync? Thanks to all those who have already commented on my question. I appreciate the input/education. Best Regards, -John > On Wed, Jul 21, 2021 at 3:55 PM Ulrich Windl > <ulrich.wi...@rz.uni-regensburg.de> wrote: >> >> Hi! >> >> Maybe someone feels motivated to write some article comparing the >> concepts >> * split brain >> * quorum >> * fencing >> > > Yet another one? Using your own reply "search is free". > > https://techthoughts.typepad.com/managing_computers/2007/10/split-brain-quo.html > >> There are eight possible states that I tried to illustrate on the >> attached sketch (S="Split Brain", "Q=Quorum, F=Fencing). >> >> ;-) >> >> Regards, >> Ulrich >> >> >> >>> Andrei Borzenkov 21.07.2021, 07:52 >>> >> >> On 21.07.2021 07:28, Strahil Nikolov via Users wrote: >> > Hi, >> > consider using a 3rd system as a Q disk. >> >> What was not clear in "Quorum is a different concept and doesn't remove >> the need for fencing"? >> >> > Also, you can use iscsi from that node as a SBD device, so you will >> have proper fencing .If you don't have a hardware watchdog device, you >> can use softdog kernel module for that. >> > Best Regards,Strahil Nikolov >> > >> > >> > On Wed, Jul 21, 2021 at 1:45, Digimer<li...@alteeve.ca> wrote: On >> 2021-07-20 6:04 p.m., john tillman wrote: >> >> Greetings, >> >> >> >> Is it possible to configure a two node cluster (pacemaker 2.0) >> without >> >> fencing and avoid split brain? >> > >> > No. >> > >> >> I was hoping there was a way to use a 3rd node's ip address, like >> from a >> >> network switch, as a tie breaker to provide quorum. A simple >> successful >> >> ping would do it. >> > >> > Quorum is a different concept and doesn't remove the need for fencing. >> > >> >> I realize that this 'ping' approach is not the bullet proof solution >> that >> >> fencing would provide. However, it may be an improvement over two >> nodes >> >> alone. >> > >> > It would be, at best, a false sense of security. >> > >> >> Is there a configuration like that already? Any other ideas? >> >> >> >> Pointers to useful documents/discussions on avoiding split brain with >> two >> >> node clusters would be welcome. >> > >> > https://www.alteeve.com/w/The_2-Node_Myth >> > >> > (note: currently throwing a cert error related to the let's encrypt >> > issue, should be cleared up soon). >> > >> > >> > _______________________________________________ >> > Manage your subscription: >> > https://lists.clusterlabs.org/mailman/listinfo/users >> > >> > ClusterLabs home: https://www.clusterlabs.org/ >> > >> >> _______________________________________________ >> Manage your subscription: >> https://lists.clusterlabs.org/mailman/listinfo/users >> >> ClusterLabs home: https://www.clusterlabs.org/ >> >> _______________________________________________ >> Manage your subscription: >> https://lists.clusterlabs.org/mailman/listinfo/users >> >> ClusterLabs home: https://www.clusterlabs.org/ > _______________________________________________ > Manage your subscription: > https://lists.clusterlabs.org/mailman/listinfo/users > > ClusterLabs home: https://www.clusterlabs.org/ > > _______________________________________________ Manage your subscription: https://lists.clusterlabs.org/mailman/listinfo/users ClusterLabs home: https://www.clusterlabs.org/
