[ClusterLabs] QDevice vs 3rd host for majority node quorum

[Klaus Wenninger]

On Tue, Jul 13, 2021 at 9:56 PM Strahil Nikolov <hunter86_bg at yahoo.com>
wrote:

> In some cases the third location has a single IP and it makes sense to use
> it as QDevice. If it has multiple network connections to that location -
> use a full blown node .

If you are intending to use watchdog-fencing via sbd with a short
watchdog-timeout
that might speak for a full blown node as well. When using QDevice
quorum-state
update may occur with a different delay (up to roughly 30s using the
default) which
requires watchdog-timeout to be long enough for the nodes to survive till
that is
settled and stonith-watchdog-timeout to be even longer to prevent
split-brain.

>
> Best Regards,
> Strahil Nikolov
>
> On Tue, Jul 13, 2021 at 20:44, Andrei Borzenkov
> <arvidjaar at gmail.com> wrote:
> On 13.07.2021 19:52, Gerry R Sommerville wrote:
> > Hello everyone,
> > I am currently comparing using QDevice vs adding a 3rd host to my
> > even-number-node cluster and I am wondering about the details concerning
> network
> > communication.
> > For example, say my cluster is utilizing multiple heartbeat rings. Would
> the
> > QDevice take into account and use the IPs specified in the different
> rings? Or
>
> No.
>
> > does it only use the one specified under the quorum directive for
> QDevice?
>
> Yes. Remote device is unrelated to corosync rings. Qdevice receives
> information of current cluster membership from all nodes (point of
> view), computes partitions and selects partition that will remain quorate.
>
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