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

Jehan-Guillaume de Rorthais jgdr at dalibo.com
Thu Jul 22 06:05:37 EDT 2021

On Wed, 21 Jul 2021 22:02:21 -0400
"Frank D. Engel, Jr." <fde101 at fjrhome.net> wrote:

> In OpenVMS, the kernel is aware of the cluster.  As is mentioned in that 
> presentation, it actually stops processes from running and blocks access 
> to clustered storage when quorum is lost, and resumes them appropriately 
> once it is re-established.
> In other words... no reboot, no "death" of the cluster node or special 
> arrangements with storage hardware...  If connectivity is restored, the 
> services are simply resumed.

Well, when losing the quorum, by default Pacemaker stop its local resources.
Considering a clustered storage, the resources are the lock manager, iscsi or
some other mean, FS etc.

However, if the resources stop actions doesn't succeed, THEN the node reset
itself. Should your cluster have active fencing, the node might be reset by some
external mean.

As Digimer wrote, «Quorum is a tool for when things are working predictably».
To do some rewording in regard with the current topic: if Pacemaker is able to
stop its resources after a quorum lost, it will not reboot, no "death" either.

> I had a 3-node OpenVMS cluster running virtualized at one point on the 
> hobbyist license and my cluster storage for that setup was simply to 
> mirror the disks across the three nodes (via software which is 
> integrated into OpenVMS); almost like RAID 1 across the network.  If I 
> "broke" the cluster and one of the servers lost quorum (due to 
> connectivity) it would just sit and wait for the connectivity to be 
> restored, then resync the storage and pick up essentially where it left off.

I believe this might be possible using a Pacemaker stack. However, I never
built such a cluster. So hopefully some other people around there with more
experience on clustered FS will infirm or confirm with some more details.


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