[Linux-cluster] GFS+DRBD+Quorum: Help wrap my brain around this

[Andrew Gideon]

On Wed, 2010-11-17 at 21:02 +0000, Colin Simpson wrote:
> On a two node non-shared storage setup you can never fully guard against
> the scenario of node A being shutdown, node B then being shutdown later.
> Then node A being brought up and having no way of knowing that it has
> the older data than B, if B is still down. 

I was under the impression that this was solved by adding in the quorum
disk.  Is that not correct?

[...]

> Three nodes just adds needless complexity from what you are saying. 

I thought that a third node could be acting as a "quorum server".  If A
can still reach that third node (C), then A and C have quorum.  The same
is true if one replaced A with B.  If A and B retain contact with each
other, but lose touch with C, quorum still exists.

You're right, though, that this doesn't solve the scenario you described
above.  Solving that by adding a third node would involve having C
somehow inform A and B which amongst them had been up most recently.  A
quorum disk would be simpler *if* the quorum disk solves this problem.

Does it?

How does this problem get solved in the DRBD world w/o an additional
layer of clustering?

Thanks...

	- Andrew