System and method for implementing a file system across different storage classes in a storage system. In the method, after the fusing temperature of the fusing roller has reached a predetermined target fusing temperature, a power corresponding to an offset value or an offset power supply ratio is supplied to a heater for a predetermined power control period or a predetermined offset control period to maintain the fusing temperature of the fusing roller. Cooling channels may be provided in or on the rear of the grating spectral filter. The expandable element is disposed over the foldable element. Vertical-direction components of a force are detected on the basis of outputs of the first magnetoelectric transducers, and a horizontal-direction component of the force is detected on the basis of an output of the second magnetoelectric transducer. The seal pad and its surface may include numerous different embodiments, including having a curved profile.