An apparatus, system, and method are disclosed for differential data backup using snapshot on-write data. A snapshot module maintains an on-write data structure that captures a point-in-time or temporal instance of a data set by tracking modifications to data blocks of a data set. A backup module copies the data set to a backup data storage device as a full data set backup. In addition, the backup module copies each modified data block indicated by the on-write data structure and a differential time stamp to the backup data storage device as a differential data set backup. The full data set backup and one or more differential data set backups form a plurality of temporal instances of the data set. In one embodiment, a restore module recovers a selected instance of the data set responsive to receiving a restore command by copying the full data set backup to a target data storage device. In addition, the restore module may copy the differential data set backup to the target data storage device if the differential time stamp corresponds to a target time value.