When configuring fencing for redundant power supplies, the cluster must ensure that when attempting to reboot a host, both power supplies are turned off before either power supply is turned back on.
If the node never completely loses power, the node may not release its resources. This opens up the possibility of nodes accessing these resources simultaneously and corrupting them.
Prior to Red Hat Enterprise Linux 6.8, you needed to explicitly configure different versions of the devices which used either the 'on' or 'off' actions. Since Red Hat Enterprise Linux 6.8, it is now only required to define each device once and to specify that both are required to fence the node, as in the following example.
pcs stonith create apc1 fence_apc_snmp ipaddr=apc1.example.com login=user passwd='7a4D#1j!pz864' pcmk_host_map="node1.example.com:1;node2.example.com:2"
pcs stonith create apc2 fence_apc_snmp ipaddr=apc2.example.com login=user passwd='7a4D#1j!pz864' pcmk_host_map="node1.example.com:1;node2.example.com:2"
pcs stonith level add 1 node1.example.com apc1,apc2
pcs stonith level add 1 node2.example.com apc1,apc2