Abstract: One embodiment of the present invention provides a semiconductor wafer 1 which is provided with: a substrate 10 that is mainly composed of Si, a buffer layer 11 that is formed on the substrate 10 and comprises an AlN layer 11a as the lowermost layer; and a nitride semiconductor layer 12 that is formed on the buffer layer 11 and contains Ga. This semiconductor wafer 1 is configured such that the pit density of the upper surface of the AlN layer 11a is more than 0 but less than 2.4×1010 cm?2.

Abstract: A storage device is provided with: a first management section that manages a storage area provided by one or more hard disk drives on a basis of a predetermined unit created using one or more parameters; a second management section that manages, on a basis of a pool configured by at least one or more of the units, a management policy about the capacity of the pools and a threshold value of the storage capacity of the pools; a power supply control section that controls each of the hard disk drives of the unit under the management of the first management section to be in either a first turn-ON state or a second turn-ON state with a low power consumption; and a control section that selects, when the storage capacity of any of the pools exceeds the threshold value, the management policy of the pools, and any of the managed parameters considered optimum to serve as the unit of the storage area, and after making the power supply control section to change the state of the hard disk drive of the selected unit from th

Abstract: A storage device is provided with: a first management section that manages a storage area provided by one or more hard disk drives on a basis of a predetermined unit created using one or more parameters; a second management section that manages, on a basis of a pool configured by at least one or more of the units, a management policy about the capacity of the pools and a threshold value of the storage capacity of the pools; a power supply control section that controls each of the hard disk drives of the unit under the management of the first management section to be in either a first turn-ON state or a second turn-ON state with a low power consumption; and a control section that selects, when the storage capacity of any of the pools exceeds the threshold value, the management policy of the pools, and any of the managed parameters considered optimum to serve as the unit of the storage area, and after making the power supply control section to change the state of the hard disk drive of the selected unit from th