[Ocfs2-users] understanding self fencing with ocfs2

[Sunil Mushran]

In a 2 node setup, if node 0 or 1 crashes, the other node should survive.
The one issue encountered by many users was while shutting down node 0,
node 1 would fence it self. The latter was because of the sequencing of
service shutdowns. We added ocfs2-init script to handle shutdown
sequencing.

However, 1.0.2 is fairly old. We've made numerous fixes. Ideally one
should be on SP3. Infact, look for SuSE to make a new drop in the coming
weeks which will include the "certified" ocfs2 bits.

Thomas.Zimolong at bmi.bund.de wrote:
> hi list,
>
> heaving read the FAQ, I still have a problem understanding the
> self fencing thing.
> the FAQ sais:
> Q02	How does OCFS2's cluster services define a quorum? 
> A02	...
> 	A node has quorum when:
> 	* it sees an odd number of heartbeating nodes and has network
> 	  connectivity to more than half of them.
> 		or 
> 	* it sees an even number of heartbeating nodes and has network
> 	  connectivity to at least half of them *and* has connectivity
> to
> 	  the heartbeating node with the lowest node number. 
>
> and
>
> Q03	What is fencing?
> A03	Fencing is the act of forecefully removing a node from a
> cluster.
> 	A node with OCFS2 mounted will fence itself when it realizes
> that it
> 	doesn't have quorum in a degraded cluster.
> 	...
>
> with a two-node-cluster with node numbers 0 and 1, I see the following
> problem.
> if the node with node number 0 crashes and neither does heartbeat nor is
> it
> reachable via LAN, we have:
> - an "odd number of heartbeating nodes" (1, the node with number 1) but
> - no "network connectivity to more than half of them" (the only other
> node
>   is'nt reachable anymore)
> so, as I see it, no qorum = self fencing.
>
> as a result, we end up with no node at all. is this right (and is it
> meant that
> way) or is there any special algorithm in a two node environment?
>
> our config is:
> two HP DL380 G4,
> SLES9 SP2 (no SP3, because it's not supported by EMC powerpath)
> Linux bmiam112 2.6.5-7.201-bigsmp #1 SMP Thu Aug 25 06:20:45 UTC 2005
> i686 i686 i386 GNU/Linux
> all OCFS modules version 1.0.2-SLES,
> ocfs2console-0.99.14-0.3
> ocfs2-tools-0.99.14-0.3
> each with two NICs in active-standby (bond0)
>
> thanks in advance and sorry, if this is kind of a "newby-question"....
>
> greetings
> thomas zimolong
>
> Bundesministerium des Inneren
> Referat Z 6 - Funktionsbereich Anwendungsentwicklung
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> D-10559 Berlin
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> mailto:thomas.zimolong at bmi.bund.de
> http://bmi.bund.de
>
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