just be aware that the deduplication is not on the file level, but on a chunk level (for fidx/VM/block device backups, chunk size is static 4MB, for didx/CT/file level/pxar backups, it's dynamically calculacted within certain limits). so an identical file A in two containers can end up being represented as one or more chunks and be deduplicated, or end up in a chunk with file B in one container, and file C in another, and not be deduplicated. so deduplication will work more reliably with snapshots of one source (chances for the chunker to split the input stream into chunks at similar boundaries are higher).