[Pacemaker] Y should pacemaker be started simultaneously.

[Digimer]

On 06/10/14 02:11 AM, Andrei Borzenkov wrote:
> On Mon, Oct 6, 2014 at 9:03 AM, Digimer <lists at alteeve.ca> wrote:
>> If stonith was configured, after the time out, the first node would fence
>> the second node ("unable to reach" != "off").
>>
>> Alternatively, you can set corosync to 'wait_for_all' and have the first
>> node do nothing until it sees the peer.
>>
>
> Am I right that wait_for_all is available only in corosync 2.x and not in 1.x?

You are correct, yes.

>> To do otherwise would be to risk a split-brain. Each node needs to know the
>> state of the peer in order to run services safely. By having both start at
>> the same time, then they know what the other is doing. By disabling quorum,
>> you allow one node to continue to operate when the other leaves, but it
>> needs that initial connection to know for sure what it's doing.
>>
>
> Does it apply to both corosync 1.x and 2.x or only to 2.x with
> wait_for_all? Because I actually also was confused about precise
> meaning of disabling quorum in pacemaker (setting no-quorum-policy:
> ignore). So if I have two node cluster with pacemaker 1.x and corosync
> 1.x with no-quorum-policy=ignore and no fencing - what happens when
> one single node starts?

Quorum tells the cluster that if a peer leaves (gracefully or was 
fenced), the remaining node is allowed to continue providing services.

Stonith is needed to put a node that is in an unknown state into a known 
state; Be it because it couldn't reach the node when starting or because 
the node stopped responding.

So quorum and stonith play rather different roles.

Without stonith, regardless of quorum, you risk split-brains and/or data 
corruption. Operating a cluster without stonith is to operate a cluster 
in an undermined state and should never be done.

-- 
Digimer
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