This can be complicated, since the system controller arbitrates the bus. It is important to establish how the redundant controller will take over all of the failed controller's operations without disrupting system operation. The mechanism is called alternate pathing. If one system controller fails, the application is informed and can direct the system to switch to the alternate controller. The key is that the switch occurs automatically whenever a path failure is detected.
Applications can also register with the framework to be notified about specific events.
Thus, it is possible to develop enhanced applications that are fully involved with any hot swap events. This is useful for capacity upgrades. For example, it is possible to add extra LAN cards to a running system and advise the application that they are ready for use. Another important benefit of alternate pathing is that it supports dynamic reconfiguration, which allows the operating system to react to system hardware changes. The combination of alternate pathing and dynamic reconfiguration enables administrators to perform online repair and reconfiguration of servers, increasing application, or service-level, availability.