Re: Redhat without qdisk

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Hello,

I manage many cluster and I had lot of problem as long as I used quorum device.
Until I remove this, my cluster are stable. I agree whith Lon Hohberger and Ryan O'Hara point of view.

You have to ask you : Do I need specific check (heuristic) or do I need scenario like "all but one" ?
If your answer are "no", please don't use quorum device.

The only problem you have to correct will be when network communication split two nodes. Both think to have quorum and try to fence the other (split brain situation). To prevent this, last clusterv2 provides redondance ring (not officially supported on RHEL5) and RHEL6 have similare feature I think.

Regards,

-- 
  .`'`.   GouNiNi
 :  ': :  
 `. ` .`  GNU/Linux
   `'`    http://www.geekarea.fr


----- Mail original -----
> De: "Gunther Schlegel" <schlegel@xxxxxxxxx>
> À: linux-cluster@xxxxxxxxxx
> Envoyé: Lundi 16 Avril 2012 17:15:52
> Objet: Re:  Redhat without qdisk
> 
> 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
> >
> >
> >     --
> >
> >
> >     .............................................................
> >     Riege Software International GmbH  Phone: +49 2159 91480
> >     <tel:%2B49%202159%2091480>
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> >     <http://www.riege.com>
> >     Germany                            E-Mail: schlegel@xxxxxxxxx
> >     <mailto:schlegel@xxxxxxxxx>
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> >     Amtsgericht Neuss HRB-NR 4207      Christian Riege
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> >
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> 
> --
> Gunther Schlegel
> Head of IT Infrastructure
> 
> 
> 
> 
> .............................................................
> Riege Software International GmbH  Phone: +49 2159 91480
> Mollsfeld 10                       Fax: +49 2159 914811
> 40670 Meerbusch                    Web: www.riege.com
> Germany                            E-Mail: schlegel@xxxxxxxxx
> --                                 --
> Commercial Register:               Managing Directors:
> Amtsgericht Neuss HRB-NR 4207      Christian Riege
> VAT Reg No.: DE120585842           Gabriele  Riege
>                                    Johannes  Riege
>                                    Tobias    Riege
> .............................................................
>            YOU CARE FOR FREIGHT, WE CARE FOR YOU
> 
> 
> 
> 
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