What are fence methods, fence devices and fence levels and what good are they?
A node can have multiple fence methods and each fence method can have multiple fence devices. Multiple fence methods are set up for redundancy/insurance. For example, you may be using a baseboard management fencing method for a node in your cluster such as IPMI, or iLO, or RSA, or DRAC. All of these depend on a network connection. If this connection would fail, fencing could not occur, so as a backup fence method you could declare a second method of fencing that used a power switch or somesuch to fence the node. If the first method failed to fence the node, the second fence method would be employed. Multiple fence devices per method are used, for example, if a node has dual power supplies and power fencing is the fence method of choice. If only one power supply were fenced, the node would not reboot – as the other power supply would keep it up and running. In this case you would want two fence devices in one method: one for power supply A and one for power supply B. All fence devices w
