[Linux-cluster] Fencing question in geo cluster (dual sites clustering)

brem belguebli brem.belguebli at gmail.com
Fri Aug 21 09:27:07 UTC 2009


I'm trying to find out what best fencing solution could fit a dual sites

Cluster is equally sized on each site (2 nodes/site), each site hosting a
SAN array so that each node from any site can see the 2 arrays.

Quorum  disk (iscsi LUN) is hosted on a 3rd site.

SAN and LAN using the same telco infrastructure (2 redundant DWDM loops).

In case something happens at Telco level (both DWDM loops are broken) that
makes 1 of the 2 sites completely isolated from the rest of the world,
the nodes at the good site (the one still operationnal) won't be able to
fence any node from the wrong site (the one that is isolated) as there is no
way for them to reach their ILO's or do any SAN fencing as the switches at
the wrong site are no more reachable.

As qdiskd is not reachable from the wrong nodes, they end up being rebooted
by  qdisk, but there is a short time (a few seconds) during which the wrong
nodes are still seing their local SAN array storage and may potentially have
written data on it.

Any ideas or comments on how to ensure data integrity in such setup ?


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