1. A disk drive comprising: a disk including a track containing a servo area on which servo data is prerecorded; a head configured to read/write data from/to said disk; an actuator mounted with said magnetic head and configured to locate said magnetic head in a target position on said disk; a servo controller configured to perform a servo control operation for driving said actuator and locating said magnetic head in the target position on said disk; a memory configured to store an initial learning value for determining a servo compensation value required when the servo control operation is performed; and a learning controller configured to determine whether the initial learning value is valid and inhibit a learning operation from being performed when the initial learning value is valid as a determination result.