1. A method of collapsing derivative versions of ancestor data volumes, the method comprising: responsive to an instruction to collapse a derivative version of an ancestor data volume into the ancestor data volume, determining if a characteristic of the derivative version of the ancestor data volume satisfies a criteria relative to a characteristic of the ancestor data volume; and, if the characteristic of the derivative version satisfies the criteria, merging the ancestor data volume into the derivative version of the ancestor data volume to form an updated derivative version and establishing the updated derivative version as the ancestor data volume.