rsync question

[R Kimber]

I've been using rsync to create an exact backup copy of my music
collection onto another disk.  I recently decided that I wanted to change
the directory structure of the collection and, to prevent rsync having to
spend hours deleting and copying the large files between the disks, I spent
some time making the changes manually on each disk.  However, the next time
the backup script ran rsync it ran for five hours.  The two disks were identical.
So what was it doing?  Or, rather, what was I doing wrong? I've clearly
misunderstood rsync. I thought that if it saw two identical file structures
it wouldn't actually do very much other than make a note of the new
structure, which even for half a TB shouldn't take all that long.

- Richard.
-- 
Richard Kimber