[ClusterLabs] DRBD failover in Pacemaker

[Digimer]

On 08/09/16 11:54 PM, Dmitri Maziuk wrote:
> On 2016-09-08 02:03, Digimer wrote:
> 
>> You need to solve the problem with fencing in DRBD. Leaving it off WILL
>> result in a split-brain eventually, full stop. With working fencing, you
>> will NOT get a split-brain, full stop.
> 
> "Split brain is a situation where, due to temporary failure of all
> network links between cluster nodes, and possibly due to intervention by
> a cluster management software or human error, both nodes switched to the
> primary role while disconnected."
>  -- DRBD Users Guide 8.4 # 2.9 Split brain notification.
> 
> About the only practical problem with *DRBD* split brain under pacemaker
> is that pacemaker won't let you run "drbdadm secondary && drbdadm
> connect --discard-my-data" as easy as busted ancient code did.
> 
> Dima

That is true without fencing.

With 'fencing resource-and-stonith;' and a {un,}fence-handler set, DRBD
will block when the peer is lost until the fence handler script returns
indicating the peer was fenced/stonithed. In this way, the secondary
WON'T promote to Primary while the peer is still Primary. It will only
promote AFTER confirmation that the old Primary is gone. Thus, no
split-brain.

-- 
Digimer
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