When you create an EVS, the EVS is created on the node selected in the Preferred Node list. However, the node that hosts the EVS might change because of node failure, network exhaustion, or other network issues. In this situation the node that is hosting the EVS (the current node) and the preferred node are no longer the same.
You can change the preferred node at any time by setting the node to be the same as the current node or by selecting another node as the preferred node.