[Ocfs2-users] understanding self fencing with ocfs2

[Thomas.Zimolong@bmi.bund.de]

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
Alt-Moabit 101 D
D-10559 Berlin
Fon 01888 681 2383
Fax 01888 681 5 2383
mailto:thomas.zimolong at bmi.bund.de
http://bmi.bund.de