Abstract:
According to one embodiment, a control unit writes data in a write buffer to a first semiconductor storage device, and requests the first semiconductor storage device to start a background operation. The control unit writes the data to a second semiconductor storage device, and requests the second semiconductor storage device to start a background operation. When the first semiconductor device is in a busy state because of the write operation or the background operation, the control unit reads data from either the second semiconductor storage device or the write buffer.