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

[Christopher Smith <csmith@xxxxxxxxxxxxxxxx>]

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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