Server system and a power control method in a server system

To provide a blade server capable of expanding disks of any servers in one chassis, the blade server has one or more server modules, one or more storage modules, a management module for managing the whole of the server, and a back plane via which a signal is transmitted among the modules wherein the server modules, the storage modules, and the management module are installed in slots. The server modules and the storage modules are interconnected via a disk interface on the back plane. Each of the server modules and the storage modules has a module management unit that controls a power in the its own module, and the module management unit controls the power in the its own module according to a power control signal sent from the management module.