By default, the SECONDARY CONTROLLER IP text box is set to none. This implies that by default, the storage device being monitored supports a single controller only. Sometimes, a storage device could be configured with two controllers i.e., say for e.g., controller 1 and controller 2, so as to provide fail-over services - in other words, if the controller 1 is down, then the controller 2 will take over to provide the critical storage services. In this case, you can provide the IP address of the controller 2 in the SECONDARY CONTROLLER IP text box.