[Pacemaker] Not unmoving colocated resources can provoke DRBD split-brain
Digimer
lists at alteeve.ca
Thu May 22 18:10:43 CEST 2014
On 22/05/14 12:08 PM, Robert Dahlem wrote:
> Hi,
>
> On 22.05.2014 16:59, Digimer wrote:
>
>> I can't speak to the pacemaker issue, but I can say that a proper
>> stonith config in pacemaker and fencing config in drbd would prevent a
>> split-brain. This would cause a node to reboot in this scenario, so you
>> still need to resolve it, but a reboot is a heck of a lot better than a
>> split-brain.
>
> And what exactly would be the sufficient cause for fencing in this scenario?
>
> Regards,
> Robert
If DRBD detects a split-brain is about to happen, it will block and call
it's fence handler (fencing resource-and-stonith;). In pacemaker setups,
this is done via the crm-fence-peer.sh handler. It will take the DRBD
fence request and pass it up to pacemaker. Once pacemaker confirms the
peer is fenced, the surviving node will unblock and resume operation,
thus avoiding a split-brain.
This still leaves the cause of the initial issue unresolved, but it does
make the consequences of that issue far less damaging.
--
Digimer
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