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

[Ulrich Windl]

Hi!

Maybe someone feels motivated to write some article comparing the concepts
* split brain
* quorum
* fencing

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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