A disk drive is disclosed employing a primary actuator for rotating an actuator
arm about a pivot in coarse movements, and first and second secondary actuators
coupled to the actuator arm for actuating first and second heads in fine movements.
A servo control system generates a first control signal applied to the first secondary
actuator to position the first head over the first disk surface in fine movements
while accessing the first disk surface. The servo control system phase shifts the
first control signal by a predetermined phase to generate a second control signal
applied to the second secondary actuator to attenuate excitation of at least one
arm vibration mode.