[Linux-cluster] Cluster not starting backup after reboot
jparsons at redhat.com
Tue Sep 11 14:32:48 UTC 2007
James Wilson wrote:
> I think I have the wrong syntax for fencing xen. Do I add
> <fence_xvmd/> to the config file or <xvmd/>?
The <fence_xvmd/> tag should be in the cluster.conf file as a child of
the <cluster> tag, in the dom0 cluster. This just tells the outside
cluster that vm fencing is going to be employed, so the fence_xvm daemon
is started and begins listening for distress from the virtual cluster it
BTW, I am pretty sure that if you include this tag and you do NOT have a
virtual cluster set up (yet), then nothing bad happens except that a few
cpu cycles are stolen from the dom0 machine running the daemon for
nothing. The inverse, however, is not true. A virtual cluster cannot be
depended upon without the daemon running on the physical host(s).
I hope this explanation buys you some insight. The simple reason for all
of this, is that DomU machines do not know they are virtual and they
cannot call 'vm destroy' on another vm even if they did know. They call
the fence_xvm fence agent when there is trouble, and this agent calls
out to the fence_xvm daemon running in the outer physical cluster and
asks it to please shut a particular VM down.
Perhaps xen kernels should include Kierkagaard and Sarte libraries for
helping them deal with their isolation, alienation, and dreaded lonliness.
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