[Linux-cluster] GFS over AOE without fencing?

[Jayson Vantuyl]

It is supposedly possible to script using the mask command to block  
servers on individual MAC address to the AoE storage.  While this is  
often offered by Coraid support as an option, I've not seen anyone  
implement it.  To be sure, I have my doubts about it anyways, give  
that the utility that you automate (cec) does not exactly provide an  
API (you actually are writing directly into the unit's console!).

On Apr 17, 2007, at 8:05 AM, Kadlecsik Jozsi wrote:

> 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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-- 
Jayson Vantuyl
Systems Architect
Engine Yard
jvantuyl at engineyard.com


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