[Linux-cluster] GFS+DRBD+Quorum: Help wrap my brain around this
ag8817282 at gideon.org
Fri Nov 19 17:48:22 UTC 2010
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.
How does this problem get solved in the DRBD world w/o an additional
layer of clustering?
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