[ClusterLabs] Antw: Re: 2-Node Cluster Pointless?

[Andrei Borzenkov]

22.04.2017 23:33, Dmitri Maziuk пишет:
> On 4/22/2017 12:02 PM, Digimer wrote:
> 
>> Having SBD properly configured is *massively* safer than no fencing at
>> all. So for people where other fence methods are not available for
>> whatever reason, SBD is the way to go.
> 
> Now you're talking. IMO in a 2-node cluster, a node that kills itself in
> response to, say, losing link on eth0 is infinitely preferable to a node
> that tries to shoot the other node when it can't ping it.
> 

How do you know whether node actually killed itself? How do you know
when it is safe to takeover resources from this node?

As a real life example (not Linux/pacemaker) - panicking node flush
eddisk buffers, so it was not safe to access shared filesystem until
this was complete. This could take quite a lot of time, so without agent
on *surviving* node(s) that monitors and acknowledges this process this
resulted in data corruption.

The problem is not so much how to put node in known state, but how other
node(s) can ensure it was done.

> This way you can also start with a one-node cluster and do the induction
> thing.
> 
> Now all you need is to separate the monitors from services so you can
> easily monitor things the cluster didn't start (like that eth0 above),
> and it'll all start making sense.
> 
> Dima
> 
> 
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