OT: rsync question

[James Pifer]

Quick rsync question. I have a whole bunch of data that I rsync to
another machine for backup purposes. I had to rebuild the primary system
and I copied all the data back to it from the backup. Now when I run the
rsync script it wants to recopy everything, even though it's already
there on both the primary and backup system. 

Are there any options on rsync to tell it to look at what's already
there and figure that out without recopying the whole thing? I looked at
the options and it wasn't obvious to me how to do this. 

My script looks like this:
rsync -av0 --progress --delete --exclude=nice_names /sourcedir
/mnt/destdir

Any help is appreciated. 

James