The Diagnose "Split Brain Recovery" is used to repair a Split Brain State in Cluster Mode.
A Split Brain may occur, if the connection over the heartbeat is not available and both nodes try to takeover the services.
In this situation, both nodes are eiter both secondary or both primary and the cluster fails.
The diagnose can be used to recover the cluster from this failure state.
The node survivor (the one that was the active node, before the error occured) can be selected.
If the Diagnose cannot repair the cluter, the cluster needs to be created again.
It is highly recommended to use a physical connection for the heartbeat by using a cross over cable.
Using a switch between the nodes for the heartbeat results in this error, if the switch is rebooted while doing a maintenance on the switch itself.
If it is necessary to use a Switch for the heartbeat, the passive node should be shutdown while doing a maintenance on the switch.