[DRBD-user] [Linux-ha-dev] ocf:linbit:drbd incorrectly handles split brain

Lars Ellenberg lars.ellenberg at linbit.com
Thu Jan 13 19:42:28 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Thu, Jan 13, 2011 at 06:53:54PM +0100, Lars Marowsky-Bree wrote:
> On 2011-01-05T15:46:54, Florian Haas <florian.haas at linbit.com> wrote:
> > Run Pacemaker on Heartbeat, and use dopd, and this won't happen.
> Hi Florian,
> is there any missing functionality in the pacemaker integration?

The main difference is that dopd would, once invoked, actually write the
outdated information into the peers meta data (provided that peer is
reachable and it's metadata still writeable).

The "crm fence peer" thingy does not, but creates a constraint only.

I'm unsure how the OP got into the split brain situation, so I cannot
comment about what needs to be changed to not get there, or if/how it
was avoidable.

I'm also not sure what exactly was expected:
>>> however, i would expect pacemaker/the ra to do something about it.                                                                                                                                             
>>> e.g. create a location constraint to not run drbd on the                                                                                                                                                       
>>> secondary/consistent node.

But the location contraint is not generated by the ocf ra,
and must not be.  That's what the fence-peer hook of drbd is for.

I wrote a lengthy email in the past about "does drbd really need stonith",
which deals a bit with resource level fencing.

I'm not aware of missing functionality in the pacemaker integration
compared to the dopd solution.

But resource level fencing (wether using dopd or crm-fence-peer)
is not trivial to get it right.  That is partially because what is right
is not clearly defined, and may well change with different requirements.

As I tried to explain in above linked post,
stonith alone does not help, either.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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