A hard link problem

[m.roth2006 at rcn.com]

We're backing up using rsync and hard links. The problem is that the fs is filling up *fast*.

According to df, 
154814444 108694756  38255576  74%
According to du -s -k, I've got 123176708 in use, which appears larger (unless it's too early in the morning for me to read that right).

Now, ls -Ri | wc -l on one directory shows 10765, while ls -Ri | sort -u | wc -l in the same directory shows 3274, so yeah, there are a lot of hard links. What I need to figure out, so that we don't blow out the filesystem, is how much space is *really* in use. I'd like something a bit faster and more elegant than, say, ls -Ri | awk '{print $!;}' > filelist, and then a shell script to loop 
find /backup -inum $fromlist -ls | awk '{print $7;}' > total, and then awk '{total += $1;}END { print total;}' total

That would be a mess....

Suggestions?

      mark