TECHNIQUE TO COMPUTE DELTAS BETWEEN ANY TWO ARBITRARY SNAPSHOTS IN A DEEP SNAPSHOT REPOSITORY

A differencing technique enables efficient retrieval of data from one of a substantial number of point-in-time images (e.g., snapshots) maintained over substantially long periods of time in a long-term storage service (LTSS) of an archival storage system. The LTSS efficiently retrieves the data by computing differences or deltas between any two arbitrary snapshots in accordance with a differencing procedure. According to the technique, the differencing procedure operates on one or more index tree structures configured to translate a logical offset range of snapshot data in a snapshot address space (e.g., of a file system) to a data object address space (e.g., of an object store hosting the snapshot data).