Garbage collection is often performed in data storage devices that implement uni-directional write policies. For example, some non-volatile solid-state memory devices and shingled disk drives both program or write data to the media in one direction, whether the incoming data from the host has random or sequential logical addresses. Because data for logical addresses can be located at any physical location, garbage collection is needed to reclaim locations on the media that no longer contain valid data for future writes. For example, in a shingled disk drive, if a track stores both valid and invalid data, the valid data may be copied by the controller as part of garbage collection to a new location so that the entire track can be made available for future write operations.