Patterned disk medium for vertical magnetic recording, and magnetic disk drive with the medium

A magnetic disk drive comprising:

• a patterned disk medium for vertical magnetic recording, the patterned disk medium including
• a disk-shaped flat substrate including a first surface and a second surface located an opposite side of the first surface;
• first servo pattern areas provided on the first surface of the substrate and each including portions provided with magnetic members and portions provided with no magnetic members, the magnetic members of the first servo pattern areas being magnetized in a direction perpendicular to the first surface and the second surface;
• and
• second servo pattern areas provided on the second surface of the substrate and each including portions provided with magnetic members and portions provided with no magnetic members, the magnetic members of the second servo pattern areas being magnetized in a same direction as the direction of magnetization of the magnetic members of the first servo pattern areas, a magnetic polarity of surfaces of the magnetic members of the second servo pattern areas being different from a magnetic polarity of surfaces of the magnetic members of the first servo pattern areas;
• a first head located, corresponding to the first surface of the disk medium;
• a second head located, corresponding to the second surface of the disk medium;
• and
• a main controller configured to control change from the first head to the second head, and change from the second head to the first head, the main controller also controlling, during the head change, reverse of polarity of a signal reproduced by a changed one of the first head and the second head, wherein during the head change, the main controller is configured to set a servo search mode which enables timing of passing of servo pattern areas just below the changed head to be estimated, the servo pattern areas being included in the first servo pattern areas and the second servo pattern areas and corresponding to the changed head.