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| Seeding and I/O fencing | ||
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When I/O fencing starts up, a check is done to make sure the systems that have keys on the coordinator points are also in the GAB membership. If the gabconfig command in /etc/gabtab allows the cluster to seed with less than the full number of systems in the cluster, or the cluster is forced to seed with the gabconfig -c -x command, it is likely that this check will not match. In this case, the fencing module will detect a possible split-brain condition, print an error and HAD will not start.
It is recommended to let the cluster automatically seed when all members of the cluster can exchange heartbeat signals to each other. In this case, all systems perform the I/O fencing key placement after they are already in the GAB membership.