We'd like to be able to snapshot a filesystem and distribute it over the network. Subsequently we'd like to distribute later snapshots, with only the differences being transmitted. Our goal is to use this to replicate read-only filesystems to multiple NFS servers, to improve reliability and aggregate bandwidth for rarely-changing data and to allow data to be moved closer to widely distributed clients. For those purposes, it's best if NFS filehandles stay the same across replicas. NFS filehandles depend on inode and generation numbers that aren't preserved by copying at the filesystem level, so we need either block-level or filesystem-specific tools. thin_delta in device-mapper-persistent-data appears to be a start on this.