[ClusterLabs] SBD & Failed Peer

[Andrew Beekhof]

> On 9 Sep 2015, at 12:13 am, Ken Gaillot <kgaillot at redhat.com> wrote:
> 
> On 09/07/2015 07:48 AM, Jorge Fábregas wrote:
>> On 09/07/2015 03:27 AM, Digimer wrote:
>>> And this is why I am nervous; It is always ideal to have a primary fence
>>> method that has a method of confirming the 'off' state. IPMI fencing can
>>> do this, as can hypervisor-based fence methods like fence_virsh and
>>> fence_xvm.
>> 
>> Hi Digimer,
>> 
>> Yes, I thought that confirmation was kind of sacred but now I know it's
>> not always possible.
>> 
>>> I would use IPMI (iLO, DRAC, etc) as the primary fence method and
>>> something else as a secondary, backup method. You can use SBD + watchdog
>>> as the backup method, or as I do, a pair of switched PDUs (I find APC
>>> brand to be very fast in fencing).
>> 
>> This sounds great.  Is there a way to specify a primary & secondary
>> fencing device?  I haven't seen a way to specify such hierarchy in
>> pacemaker.
> 
> Good news/bad news:
> 
> Yes, pacemaker supports complex hierarchies of multiple fencing devices,
> which it calls "fencing topology". There is a small example at
> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#_advanced_stonith_configurations
> 
> Unfortunately, sbd is not supported in fencing topologies.

Another way to look at it, is that sbd is only supported in fencing topologies - just not explicit ones.
Self-termination is always the least best option, so we’ll only use it if all other options (including topologies) are exhausted.
But we’ll do so automatically.

> Pacemaker
> hooks into sbd via dedicated internal logic, not a conventional fence
> agent, so it's treated differently. You might want to open an RFE bug
> either upstream or with your OS vendor if you want to put it on the
> radar, but sbd isn't entirely under Pacemaker's control, so I'm not sure
> how feasible it would be.
> 
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