Comment 5 for bug 610399

Actually, it looks like it might be due to a bug in rsync.
I've been unable to do a full backup for a while now thanks to the "broken pipe" error of rsync (which is caused by a failed assert in the hardlink code).
Turns out rsync had a bugfix release 3.0.8 that came out a month ago and features fixes such as:
"Fixed a data-corruption issue when preserving hard-links without
      preserving file ownership, and doing deletions either before or during
      the transfer (CVE-2011-1097). This fixes some assert errors in the
      hard-linking code, and some potential failed checksums (via -c) that
      should have matched."
which seemed right on the money (full list here: http://rsync.samba.org/ftp/rsync/src/rsync-3.0.8-NEWS )

Anyway, I compiled and installed that version and was immediately able to do a full backup without any issue.

Add that to the list of things to try if Artem's solution doesn't fix it for you.