[Linux-cluster] 2-node cluster fence loop

Arun G Nair arun.nair at dimensiondata.com
Thu Jun 12 14:29:06 UTC 2014

We have multicast enabled on the switch. I've also tried the multicast.py
tool from RH's knowledge base to test multicast and I see the expected
output, though the tool uses a different multicast IP( guess that shouldn't
matter). I've tried increasing the post_join_delay to 360 seconds to give
me enough time to check everything on both the nodes. One node still gets
fenced. `clustat` output says the other node is offline on both servers. So
one node can't see the other one ? This again points to issue with
multicast. Any other clues as to what/where to look ?

On Wed, Jun 11, 2014 at 8:33 PM, Digimer <lists at alteeve.ca> wrote:

> On 11/06/14 10:48 AM, Arun G Nair wrote:
>> Hello,
>>     What are the reasons for fence loops when only cman is started ? We
>> have an RHEL 6.5 2-node cluster which goes in to a fence loop and every
>> time we start cman on both nodes. Either one fences the other. Multicast
>> seems to be working properly. My understanding is that without rgmanager
>> running there won't be a multicast group subscription ? I don't see the
>> multicast address in 'netstat -g' unless rgmanager is running. I've
>> tried to increase the fence post_join_delay but one of the nodes still
>> gets fenced.
>> The cluster works fine if we use unicast UDP.
>> Thanks,
> Hi,
>   When cman starts, it waits post_join_delay seconds for the peer to
> connect. If, after that time expires (6 seconds by default, iirc), it gives
> up and calls a fence against the peer to put it into a known state.
>   Corosync is what determines membership, and it is started by cman. The
> rgmanager only handles resource start/stop/relocate/recovery and has
> nothing to do with fencing directly. Corosync is what uses multicast.
>   So as you seem to have already surmised, multicast is probably not
> working in your environment. Have you enabled multicast traffic on the
> firewall? Do your switches support multicast properly?
> digimer
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> Digimer
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Arun G Nair
Sr. Sysadmin
Dimension Data | Ph: (800) 664-9973
Feedback? We're listening <http://www.surveymonkey.com/s/XRCYXBH>
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