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Re: [Linux-cluster] GFS over AOE without fencing?



Hi Bryn,

On Tue, 17 Apr 2007, Bryn M. Reeves wrote:

> > Assuming a dedicated VLAN which servers only AOE and GFS traffic among 
> > the Coraid boxes and the GFS hosts, is there any need for fencing at all?
> > 
> > What are the hidden traps behind such setups?
> > 
> > Best regards,
> > Jozsef
> 
> If you are using GFS on shared storage then you need fencing. Period.
> 
> The only way you can guarantee data integrity in this scenario is by
> completely cutting a failed or misbehaving node off from the storage;
> either by power cycling it or having the storage reject its access.
> 
> Otherwise, imagine a situation where a node hangs for some reason and is
> ejected from the cluster. At this point none of its locks for the shared
> data are valid anymore. Some time later, the node recovers from the hang
> and begins flushing writes to the storage -> corruption.

I see - the sentences above make much more clearer why fencing is needed.
Thank you the explanation - and the hint for the possibility to reject 
the access at the storage itself!
 
Best regards,
Jozsef
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