Disk drive defining guard bands to support zone sequentiality when butterfly writing shingled data tracks

A disk drive is disclosed wherein a plurality of zones are defined on first and second disk surfaces, wherein each zone comprises a plurality of data tracks. Data is written to the data tracks of a first plurality of the zones on the first and second disk surfaces in an interleaved manner, in a first radial direction, and in a shingled manner. Data is written to the data tracks of a second plurality of the zones on the first and second disk surfaces in an interleaved manner, in a second radial direction opposite the first radial direction, and in a shingled manner. At least one guard band is defined at a boundary between a first zone and a second zone in the second plurality of zones on the first disk surface, wherein the guard band comprises at least one unused data track.