The disclosed techniques that can use deduplication information on a source computer platform to improve the process of performing data backups or restoration from/to the computer platform. In one example aspect, a data backup operation can re-use some of the work already done by a source computer's deduplication system. For example, a storage operation could read a deduplication database on the source computer platform to determine the duplicativeness of a given data chunk being transferred to a backup storage system, without having to perform computations such as data chunk hashing and comparison with previously generated hashes. The technique may additionally or alternatively reuse hashes generated by the source computer during deduplication of the data file on the source computer's file system during deduplication at the external backup storage system.