A method for releasing storage space in a space-efficient volume is disclosed. In one embodiment, such a method includes maintaining, for a space-efficient volume, a bitmap comprising a bit for each track in the space-efficient volume. A host system indicates whether a track is one of used and unused by marking the corresponding bit in the bitmap. A storage controller reads the bitmap and frees tracks from the space-efficient volume that the bitmap indicates are unused. In certain embodiments, the bitmap is stored on the space-efficient volume. For example, the bitmap may be appended to a volume table of contents (VTOC) stored on the space-efficient volume. A corresponding system and computer program product are also disclosed.