On Fri, Jul 23, 2021 at 8:55 AM Ulrich Windl < ulrich.wi...@rz.uni-regensburg.de> wrote:
> >>> "john tillman" <jo...@panix.com> schrieb am 22.07.2021 um 16:48 in > Nachricht > <1175ffcec0033015e13d11d7821d5acb.squir...@mail.panix.com>: > > There was a lot of discussion on this topic which might have overshadowed > > this question so I will ask it again in case someone missed it. > > > > It comes from a post (see below) that we were pointed to here by Andrei: > > > > Is there something like the described "ping tiebreaker" in the current > > world of pacemaker/corosync? > > Maybe explain how it should work: > If the two nodes cannot rech each other, but each can reach the ping node, > which node has the quorum then? > Guess both - which is what is played down as 'disadvantage' in the description below ;-) > > > > > Best Regards, > > ‑John > > > >> Interesting read. Thank you for providing it! > >> > >> In this follow up post > >> > > > https://techthoughts.typepad.com/managing_computers/2007/10/more > ‑about‑quor.htm > > > l > >> 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.htm > > > l > >>> > >>>> 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/ > >> > >> > > > > > > _______________________________________________ > > 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/ >
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