Generally described, one or more aspects of the present application relate to a public snapshot service for creating and managing block-level snapshots. For example, the public snapshot service can create a snapshot based on (i) a specification of a parent snapshot to be used as a basis for a given snapshot, and (ii) a specification of the data blocks to be backed up in the given snapshot. The data blocks in the snapshot may be stored in a specific storage path structure that facilitates computation of a block difference with respect to the parent snapshot.