A disk drive is disclosed having a servo control system optimized for
faster determination of repeatable runout (RRO) correction values. Each
circumferential track on a magnetic disk exhibits total runout having an
RRO component and a nonrepeatable runout (NRO) component. The control
system generates a control signal for positioning a transducer head
during a track following operation based on distributed position
information defining the followed track. PES values are calculated based
on the distributed servo position information read during a track
following operation. The first servo-loop compensator processes the PES
values during normal data access operations and has a first transfer
function that is optimized with respect to a variance of the total
runout. The second servo-loop compensator processes the PES values during
a RRO calibration operation and has a second transfer function that is
optimized with respect to a variance of the NRO component.