Hi,
But if you have problem with your storage it's normale the node goes
fenced, because your cluster services depends on storage
Well, no, my clustered services do not depend on SAN storage.
Or maybe you wold like to have a cluster running without san disk
I need the qdisk for two reasons:
- heuristics
- to safely achieve quorum in a two-node-cluster if only one node is up.
regards, Gunther
Il giorno 13 aprile 2012 11:20, Gunther Schlegel <schlegel@xxxxxxxxx
<mailto:schlegel@xxxxxxxxx>> ha scritto:
Hi Lon,
> > Why redhat made the qdisk as Tie-breakers and some people from
support
> > say it's one optional or some time says is not needed?
>
> It is optional and is often not needed. It was developed really
for two purposes:
>
> - to help resolve fencing races (which can be resolved using
delays or other tactics)
>
> - to allow 'last-man-standing' in >2-node clusters.
>
> With qdiskd you can go from 4 to 1 node (given properly configured
heuristics). The other 3 nodes then, because heuristics fail, can't
"gang up" (by forming a quorum) on the surviving node and take over
- this means your critical service stays running and available. The
problem is that, in practice, the "last node" is rarely able to
handle the workload.
>
> This behavior is obviated by features in corosync 2.0, which gives
administrators the ability to state that a -new- quorum can only
form if all members are present (but joining an existing quorum is
always allowed).
Is this in RHEL6? I am still trying to solve the following situation:
- 2 node cluster without need for shared storage (no gfs)
- qdiskd in place because of the heuristics.
- Cluster is fine if both nodes have network communication and
heuristics reach the minimum score.
Problem: if the shared storage the qdisk resides on becomes
unavailable (but everything else is fine) a node will be fenced. It
actually happens at the time the shared storage comes back online,
the node re-establishing the storage link first wins and fences the
other one. I try to mitigate that with loooong timeout settings, but
therefore a necessary cluster switch eviction is also delayed.
I would really appreciate if the qdiskd would withdraw it's quorum
vote and not do any fencing at all. The cluster would survive as
quorum is also gathered if the cluster network connection is
established.
best regards, Gunther
Gunther Schlegel
Head of IT Infrastructure
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