[Linux-cluster] does fencing require a dedicated network ?

[Carlos Maiolino]

Hi Pierre

On Fri, Apr 16, 2010 at 01:52:55PM +0200, Pierre Amadio wrote:
> Hi there !
> 
> A customer is planning to use our cluster suite (most probably with 2
> nodes cluster running RHEL5 cluster suite).
> 
> The fencing mechanism will be some rsaII cards.
> 
> Right now, the rsaII cards are on a another  network than the one used
> for heartbeat. The problem is, it is dedicated to an admin team wich
> does not want the cluster suite solution to have access to this specific
> network. The customer does not know yet if he will accept to create a
> new network and put the rsaII cards (and only them) on it.
> 
> Would it be a problem as far as the cluster suite and the support
> coverage is concerned if those devices were available on the same
> network as the one used for heatbeat ?
> 
Yes and no, depends on the network design

> I would be tempted to say yes to both, because i dont know how one node
> could fence the other in case there was a communication problem between
> the 2 node on the heartbeat.

Depends on the problem occurrs, if both nodes (heartbeat and fence) are connected on the same switch without redundancy, and the switch fails, the cluster nodes cannot fence each other (and we still have a split-brain), but if the problem occurs in a node communication (cable problem, NIC problem, switch-port, etc) the healthy node still can send a fence signal to the failed node.

So, is a good idea to have or a redundant design (e.g. bonding connected a two separate switchs), or, separate the fence network and use a quorum disk system.



> 
> The following article seems to states it can be done (even without any
> quorum disk):
> http://kbase.redhat.com/faq/docs/DOC-16712
> 
> The article is still unverified though.
> 
> Is it ok to give the customer a green flag using a two node cluster
> (without quorum disk) where heartbeat and fencing use the same network ?
> 
> 
> -- 
> Pierre Amadio <pamadio at redhat.com>            
> Technical Account Manager                     mobile: +33 685 774 477
> Red Hat France SARL, 1 rue du Général Leclerc, 92047 Paris La Défense
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> 
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-- 
---

Best Regards

Carlos Eduardo Maiolino
Software Maintenance Engineer
Red Hat - Global Support Services