rsync and vfat filesystems

When I have added a few CD’S to my ogg collection I need to copy them across to my H320. This is OK if you copy the CD over as soon as it has been copied but I don’t normally work that way. We just got some CD’s for Christmas and I already had a few copied to the hard drive so as usual I use rsync to do it.
I noticed that rsync would always copy everything rather than do an update of the files. I found out that this is because of limitations on a vfat file system. The following command sorted it.
rsync -av –modify-window=1 * /mnt/usb/