A servo write method for a hard-disk drive. The method includes generating, with an input of characteristics of a magnetic-recording head and a magnetic-recording disk which are incorporated into the hard-disk drive, a yield prediction model from a correlation between yields of the hard-disk drive, and characteristics of the magnetic-recording head and the magnetic-recording disk of the hard-disk drive in a process. The method also includes predicting a yield which is obtained when each magnetic-recording head is used as a position control head, selecting as the position control head a magnetic-recording head that has a highest predicted yield, and writing a servo signal.