Coherent repeatable runout correction for reduced rpm self-servo write

A disk drive, comprising:

• a magnetic head;
• a magnetic disk with a set of servo spirals formed on a surface of the magnetic disk;
• and
• a controller configured to perform the steps of:
• while rotating the magnetic disk at a first rotational speed, controlling a radial position of the magnetic head to be at a target radial location based on a set of servo spirals formed on the surface of the magnetic disk;
• and
• while the magnetic disk is rotated at the first rotational speed and the magnetic head is controlled to be at the target radial location, for each spiral included in the set of servo spirals:
• receiving a position error signal associated with crossing the servo spiral;
• modifying the position error signal with a correction factor that is based on a first non-circularity value associated with the servo spiral at the target radial location and a second non-circularity value associated with the servo spiral at the target radial location, wherein the first non-circularity value for the spiral is determined while rotating the magnetic disk at the first rotational speed and the second non-circularity value is determined while rotating the magnetic disk at a second rotational speed that is different from the first rotational speed;
• and
• writing a set of servo wedges at the target radial location.