Compensation for repeated runout (RRO) error, such as in a data storage
device servo circuit, is preferably carried out by obtaining a population
distribution of RRO error values from at least selected ones of a subset
of tracks. An RRO error compensation value is determined for each one of
the subset of tracks when a variance characteristic of said population
distribution meets a selected criterion. Preferably, a first track of a
storage medium has a servo field at a first angular position on the
medium, a repeated runout (RRO) error compensation field at a second
angular position on the medium, and a user data field at a third angular
position on the medium. An immediately adjacent second track preferably
has a servo field at the first angular position and a user data field at
the second angular position in lieu of an RRO error compensation field.