[ClusterLabs] [EXT] Re: Two node cluster without fencing and no split brain?

[Andrei Borzenkov]

On Wed, Jul 21, 2021 at 3:55 PM Ulrich Windl
<Ulrich.Windl at 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<lists at 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).
> >
> >
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