Data storage device and servo information writing method

A data storage device comprising:

• a disk-shaped storage medium which has a data storage area and a servo area, the data storage area containing a plurality of data tracks which store user information, the servo area containing a plurality of servo tracks which store servo information for identifying positions of the plurality of data tracks;
• a hybrid head slider which supports write and read heads, the write head writing user data on the data tracks of the disk-shaped storage medium, the read head reading the user data written on the data tracks;
• and
• a rotary-type actuator which swings the hybrid head slider to position any one of the write and read heads at a target track of the disk-shaped storage medium, wherein a pitch of the servo tracks varies within a predetermined region in a radial direction of the disk-shaped storage medium.