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The I/O fencing feature protects against data corruption resulting from a failed cluster interconnect or "split brain." See "VCS Communications, Membership, and I/O Fencing" in the VCS User's Guide for details on the problems a failed interconnect can create and the protection I/O fencing provides.
I/O fencing uses SCSI-3 Persistent Reserve keys to implement data protection. The software places keys on I/O fencing coordinator and data disks. The administrator must be aware of several operational changes needed when working with clusters protected by I/O fencing. Specific shutdown procedures ensure keys are removed from coordinator disks and data disks to prevent possible difficulties with subsequent cluster startup.
Using the reboot command rather than the shutdown command bypasses shutdown scripts and can leave keys on the coordinator and data disks. Depending on the order of reboot and subsequent startup events, the cluster might warn of a possible split brain condition and fail to start up.
Workaround: Use the shutdown -r command instead of the reboot command to perform a graceful reboot for systems.