I recently had a look at a few linux deduplicated filesystems, namely opendedup, lessfs and ddumbfs to act as a backup repository storage.
I was frustrated with opendedup because if would return "filesystem full" when there was no obvious reason why the filesystem might be full. As a result, I did not feel confident that I could safely monitor the system to alert me prior to the filesystem filling up.
Lessfs was too slow in my environment using the berkelydb and tokyodb backends, and I could not get hamsterdb to make a clean filesystem