[ClusterLabs] Pacemaker newbie

[Ken Gaillot]

On Fri, 2024-09-13 at 17:32 +0200, Antony Stone wrote:
> On Friday 13 September 2024 at 17:23:59, Taylor, Marc D wrote:
> 
> > We bought a storage system from Dell and they recommended to us
> > that we
> > should use a two-node cluster
> 
> I do hope you realise that a literal two-node cluster is not a good
> idea?
> 
> If the two nodes lose contact with each other, you get a situation
> called 
> "split brain" where neither node can know what state the other node
> is in, and 
> neither node can safely take over resources.

As long as fencing is configured (and tested!), a two-node cluster is
not a problem. If the nodes lose communication, one side will fence the
other and take over all resources. (Various fencing options are
available to avoid a "death match" where both nodes fence each other.)

> 
> You should always have an odd number of nodes in a cluster, and
> provided more 
> than 50% of the nodes can see each other, they will run resources;
> any node 
> which cannot see enough other nodes to be in a group of more than 50%
> will 
> stop running resources.
> 
> > to share the storage out as either NFS or SMB.
> 
> Do they explicitly say you can do both?
> 
> It might be possible to share a single storage resource using both
> NFS and 
> SMB, but it must have some interesting file-locking capabilities.
> 
> 
> Antony
> 
-- 
Ken Gaillot <kgaillot at redhat.com>