http://sn.1w6.org/file/mk-20141012T071013-gft9ytg.html

@sazius It seems Attic also has a 'deduplication' algo that sends only changed chunks of files; this is important since I will have to use it over slow Internet connections. Attic supports encryption, as an option. But another factor is I cannot just install 'anything' on the #NAS - it's embedded Linux, and comes with (installable) rsync; there's a user-suported package for rsnapshot (but the archive is called "unstable"); Python and Perl are available, too, so rsync + scripting in one of those should work.