Greetings,
you should probably read zbackup description (available on
http://zbackup.org/) and perform backup/restore on multiple VM images.
All software that you are talking about (rdiff-backup, rsnapshot, amanda, backuppc, bacula and tons of homegrown "bash backup systems") does not provide real deduplication.
All of that symlinks/hardlinks tricks isn't deduplication at all.
We use a 64-bit modified Rabin-Karp rolling hash with sliding window that performs checking with a single-byte granularity. It was even better than ZFS deduplication.
Take a try and then we will talk about "Yet Another Incompatible Backup Paradigm(tm)" that you will probably pronounce as "next-gen backup paradigm" after you will give a try ;)
Yep, not "first next-gen backup paradigm" but "one of two opensource next-gen backup software" because all other software that performs deduplication with sliding window was closed-source proprietary systems.
Thanks!