A method of writing product servo sectors on a disk of a disk drive is
disclosed. The disk comprises a reference pattern having a plurality of
sync marks written around the disk. The sync marks are detected to
generate a sync mark detect signal, and a timing recovery measurement is
generated in response to the sync mark detect signal. A frequency control
signal is generated in response to the timing recovery measurement, and a
servo write clock is generated in response to the frequency control
signal. A feed-forward compensation value is generated in response to the
timing recovery measurement and the frequency control signal, and the
timing recovery measurement is adjusted in response to the feed-forward
compensation value to compensate for a repeatable phase error in the
timing recovery measurement. The servo write clock and the head internal
to the disk drive are used to write the product servo sectors to the
disk.