[ClusterLabs] Corosync lost quorum but DLM still gives locks

[Jean-Marc Saffroy]

Replying to myself:

On Wed, 11 Oct 2017, Jean-Marc Saffroy wrote:

> I am caught by surprise with this behaviour of DLM:
> - I have 5 nodes (test VMs)
> - 3 of them have 1 vote for the corosync quorum (they are "voters")
> - 2 of them have 0 vote ("non-voters")
> 
> So the corosync quorum is 2.
> 
> On the non-voters, I run DLM and an application that runs it. On DLM, 
> fencing is disabled.
> 
> Now, if I stop corosync on 2 of the voters:
> - as expected, corosync says "Activity blocked"
> - but to my surprise, DLM seems happy to give more locks
> 
> Shouldn't DLM block lock requests in this situation?

Apparently DLM does not care about changes in quorum until there are 
changes in membership of the process groups it is part of. In my test, the 
"voters" do not run DLM, and therefore (I suppose?) DLM does not react to 
their absence.

DLM does block lock requests when quorum is lost AND THEN there is a 
change in membership for the DLM participants, because quorum is required 
for lockspace operations.

Does that make sense?


Cheers,
JM

-- 
saffroy at gmail.com