Some power supplies support a Master/Slave relationship: When one power supply is set to master(1) and the other is set to slave(2), the master will supply all power to the cabinet, and the slave will take over if the master stops supplying power. This is useful when (for example) one supply is attached to a wall socket and the other to a battery backup. The cabinet can be directed to only draw power from batteries when there is no alternative. When both power supplies are set to master(1), the results are determined automatically. WARNING: It is up to the system administrator to ensure that at least one power supply is set to master(1). It is illegal to set all power supplies to slave(2). If this occurs, the cabinet may lose all power under certain circumstances, even if power is available. In some cases, the Master/Slave relationship cannot be configured via management; it is determined by other means, such as the slot locations in which the supplies are installed, or switches on the supplies. In this case, attempts to change the value of this variable from management will be ignored. The ConfigMode variable will have the value hardware(2) in this case. If a supply does not support (or can disable) Master/Slave functionality, the value shared(3) is returned. In this case, all ready power supplies share the load evenly. A single CPSMP110 control unit can support multiple subdevices of this type.