A method of writing product servo sectors to a disk of a disk drive is
disclosed. The disk comprises a plurality of spiral tracks, wherein each
spiral track comprises a high frequency signal interrupted at a
predetermined interval by a sync mark. The read signal from the head is
processed to detect a plurality of the sync marks in a spiral track
crossing. A timing recovery measurement is generated in response to a
selected one of the sync marks based on reliability metrics, wherein a
servo write clock is synchronized in response to the timing recovery
measurement. The read signal representing the high frequency signal in
the spiral track crossing is processed to generate a position error
signal (PES) used to maintain the head along a substantially circular
target path while using the servo write clock to write product servo
sectors along the circular target path.