Embodiments of the present invention relate to a method for manufacturing a magnetic disk unit, the method including a step of writing servo data into the magnetic disk while introducing a low-density gas having a lower density than air into the enclosure. In one embodiment, the magnetic disk unit is comprised of a magnetic disk, a magnetic head, and a voice coil motor which are accommodated in the hermetically sealed enclosure. The enclosure has a gas inlet and a gas outlet, which are provided respectively with filters attached thereto.