US Patent 8001343 Storage device with power control function

To provide a power controlling method for use in a storage device which can be operated with less power consumption, at least a storage capacity monitoring unit for monitoring the storage amount of data stored in each storage unit, a power-on unit for controlling the power-on of each storage unit, an access state monitoring unit for monitoring the state of accesses from an upper device to each storage unit, and a power-off unit for controlling the power-off of each storage unit are comprised, thereby controlling the power of a second storage unit.