One or more techniques and/or systems are provided for incremental transfer with unused data block reclamation. For example, source volume of a source storage filer may have a physical replication relationship with a destination volume of a destination storage filer. Snapshots of a file system of the source volume may be used to identify new data blocks (e.g., data blocks allocated or reallocated to a new snapshot) and/or unused data blocks (e.g., data blocks of a deleted snapshot) used to incrementally update the destination volume so that the destination volume is a mirrored replication of the source volume. In this way, new data blocks may be updated and unused data blocks may be punched out (e.g., deallocated) of the destination volume during execution of an incremental update.