[ClusterLabs] Speed up the resource moves in the case of a node hard shutdown

[Klaus Wenninger]

On 02/13/2018 01:28 PM, Maxim wrote:
> 13.02.2018 14:03, Klaus Wenninger пишет:
>> - fencing helps you turning the  'maybe the node is down - it doesn't
> > respond within x milli-seconds' into certainty that your node is dead
> > and won't interfere with the rest of the cluster
> >
> > Regards, Klaus
>
> It is clear. But will it force pacemaker to perceive that the node is
> down faster?

Let's put that differently. With fencing you can make the loss-detection
more
aggressive and thus more prone to false-positives without risking a
split-brain situation. (Actually without fencing you can never be really
sure if the other side is really gone!)
But to be honest if you are really behind sub-second detection/switchover
I'm not sure if fencing - at least with the current implementation in
pacemaker and the current selection of fencing-devices - will
give you satisfactory results.

> [Unfortunatly, I've no a hardware that implements fencing abilities
> nearby and can't try it myself]

If you don't have any of the usual fencing-devices available you might
have some kind of a shared-disk that might be usable with SBD.
For a 2-node-cluster with a single shared-disk (as in your case if I got
it correctly) assure to pick an SBD-version that has
https://github.com/ClusterLabs/sbd/commit/4bd0a66da3ac9c9afaeb8a2468cdd3ed51ad3377.
But again I doubt that this will work reliably with sub-second requirements.

>
> [Seems, it is the last question from my side that is devoted to this
> topic]
>
> Thank you and Ken for the participation!
>
> Regards,
> Maxim

Not saying I'm not interested in experiences/requirements with
pacemaker doing failovers in a sub-second or more relaxed
low-single-digit-second timeframe.
Seeing this working reliably would open up pacemaker for a
completely new class of applications.

Regards,
Klaus