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Re: [Xen-users] Re: Alternatives to cman+clvmd ?



Ferenc Wagner wrote:
Christopher Smith <csmith@xxxxxxxxxxxxxxxx> writes:

I am "managing" the shared storage [...] using cman+clvmd [...]
However, this combination seems to be horribly unreliable.  Any
network hiccup more than a lost ping or two results in cman losing
contact with the rest of the machines, which it frequently does not
regain.

This isn't inherent to cman, I've been using it for years without much
problem.  You have to handle fencing correctly, otherwise it will bite
you, no matter what timeouts you configure.  But otherwise, it's OK.

Well, I use manual fencing...

I realise this is less than ideal, but it's far more ideal to me than a xen host getting fenced and taking out twenty VMs. Especially given how frequently it seems to get to the point where it would have fenced something.

For example, failing one of the bonded NICs usually takes few
seconds for everything to 'stabilise' again on the network, but in
that time cman has lost contact with all the other nodes and often
killed itself (or bits of itself) in the process.

This shouldn't happen.  Either you misconfigured your bonding (though
a few seconds failover time doesn't sound gross), or more likely you
misconfigured cman: it's defaults aren't this strict, even.

This was actually a problem on the switches, something to do with STP - the bonding failovers were actually taking a bit over 30 seconds, so that's probably why cman was falling over.

Having said all this, managing the cluster infrastructure for so
little (clvm only) feels excessive indeed.  But I don't know any
better way (other than doing volume management on the storage side).

And volume management on the storage side brings along its own set of complications. :(

--
Christopher Smith

UNIX Team Leader
Nighthawk Radiology Services
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