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[Linux-cluster] Avoiding fencing loops with startup quorum (patch)



Hi all,
  I am managing a two-node cluster without qdisk and to avoid the
fencing loop I thought to implement a startup quorum.
The startup quorum would be the minimum total votes a node requires to
remain in the cluster after the startup process.
When cman is started on a node it joins the cluster and if the total
votes are less than the CMAN_STARTUP_QUORUM it leaves preventing
fencing to be executed.

I configured my CMAN_STARTUP_QUORUM to 2:
- When the two nodes joins the cluster together the total votes are 2;
everything is normal.
- When a node get fenced the remaining one is in quorate (cman real quorum: 1).
- When the fenced node boots up and finds the other node the total
votes are 2; everything is normal.
- When the fenced node boots up and doesn't find the other node the
total votes are 1 (< CMAN_STARTUP_QUORUM); the node leaves the
cluster, stop cman and prevent fencing.

This might be handy for booting up a remote node for maintenance and
not being worried about fencing loops.
The downside is that you can't boot a single node and having it
working alone; this situation can be considered an emergency and can
be handled manually.

The startup quorum might resolve also:

https://www.redhat.com/archives/linux-cluster/2008-June/msg00143.html
https://bugzilla.redhat.com/show_bug.cgi?id=452234

Patch in attachment. Can anyone review it?
Is anyone interested to integrate this same behaviour into cman and
the cluster.conf?

Ex:
  <cman two_node="1" expected_votes="1" startup_votes="2" />

Thanks,
-- 
Federico.

Attachment: cman_startup_quorum.patch
Description: Binary data


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