A method for manufacturing a hard-disk drive (HDD). The method for manufacturing a HDD includes writing servo tracks, and writing servo tracks into the HDD using a calculated control target value of a calculated servo pattern overlap amount. Writing servo tracks includes a first, second, third and fourth operation. The first operation includes: producing a first control equation for obtaining a servo pattern overlap amount; and, converting a root-mean-square error (RMSE) into a probability distribution. The second operation includes calculating a second control target value that results in an increased product yield, from the RMSE probability distribution. The third operation includes producing a second control equation for obtaining a calculated servo pattern overlap amount, by assigning the second control target value into the first control equation. The fourth operation includes calculating the calculated control target value using the second control equation and the magnetic-recording-head characteristic value.