[Pacemaker] again trouble with quorum (now with cman)

[Digimer]

On 12/07/13 04:26, Andrey Groshev wrote:
>
>
> 12.07.2013, 09:15, "Digimer" <lists at alteeve.ca>:
>> On 12/07/13 00:59, Andrey Groshev wrote:
>>
>>>   11.07.2013, 18:48, "Digimer" <lists at alteeve.ca>:
>>>>   You need fencing. Specifically, cman blocks when a fence is called and
>>>>   won't unblock until it's told that a fence completed successfully.
>>>>   Configure cluster.conf to use 'fence_pcmk', which tells cman to pass
>>>>   fence requests to pacemaker, and then configure (and test!) stonith in
>>>>   pacemaker.
>>>>
>>>>   If you have just two nodes, be sure to also set '<cman two_node="1"
>>>>   expected_votes="1" />'.
>>>>
>>>>   digime
>>>>
>>>>   On 11/07/13 09:35, Andrey Groshev wrote:
>>>   I understand that it may be correct to do so...
>>>   But why so difficult?
>>>   Assume, I make a small НА cluster in my garage.
>>>   And, I not have a managed switch or managed UPS.
>>>   I can not corrupt the data.
>>>   I just need to returning node as soon as possible started responding.
>>
>> First, fencing is not difficult, it's just one of the parts of
>> clustering to learn. Second, the cluster software has no concept of
>> "unimportant cluster". It treats every cluster as enterprise class.
>> Third, if a service can run on both nodes without coordination with one
>> another, then you don't need the cluster stack at all.
>>
>> Assuming you actually need to keep the service on one node or the other,
>> you need to have a way to make sure the "lost" node really is lost. You
>> are not allowed to make assumptions. "The only thing you know if what
>> you don't know". Fencing puts a node in an unknown state (disconnected?
>> frozen? crashed? blown to pieces?) and puts it into a known state,
>> "off". This ensures the service can never run on both nodes at the same
>> time.
>>
>> --
>> Digimer
>> Papers and Projects: https://alteeve.ca/w/
>> What if the cure for cancer is trapped in the mind of a person without
>> access to education?
>
> Well, without a truly fence devices, I must use fence_pcmk?

fence_pcmk is not a fence device, it simply tells cman to pass fence 
requests over to pacemaker. So you then have to be sure pacemaker can 
fence the nodes. For this, you need an actual fence device, like IPMI, 
switched PDUs, etc.

-- 
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without 
access to education?