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

Jehan-Guillaume de Rorthais jgdr at dalibo.com
Wed Jul 21 05:23:47 EDT 2021

On Wed, 21 Jul 2021 04:50:09 -0400
"Frank D. Engel, Jr." <fde101 at fjrhome.net> wrote:

> OpenVMS can do this sort of thing without a requirement for fencing (you 
> still need a third disk as a quorum device in a 2-node cluster), but 
> Linux (at least in its current form) cannot.

Yes it can, as far as what you are describing.

Pacemaker supports the following architectures without "active" fencing:

* 2 nodes + shared storage (as quorum device + poison pill)
* 3 nodes (for quorum) + watchdog

> From what I can tell the fencing requirements in the Linux solution are
> mainly due to limitations of how deeply the clustering solution is integrated
> into the kernel.

Could you explain what you mean? I'm not sure how the kernel is involved there.
The kernel itself can be the problem. That's why using softdog is discouraged.

> There is an overview here: 
> https://sciinc.com/remotedba/techinfo/tech_presentations/Boot%20Camp%202013/Bootcamp_2013_Comparison%20of%20Red%20Hat%20Clusters%20with%20OpenVMS%20Clusters.pdf

This is a quite old presentation and many things changed. I fairly sure a lot of
this content is outdated. First, corosync evolved a lot. Second RHCS now use
Pacemaker default, not CMAN based HA.


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