Jeff has some great suggestions here, but maybe one that you haven't thought of is to add yet another disk shelf (if the 720 supports it) with more disks. Then you can shuffle data around without having to totally dump/restore (burn down the village) scenario. You will have some downtime required here, just to do the re-balancing, but with more disks, you'll be able to spread the load better.
And these days, FC7/8 shelves with 36gb disks should be pretty cheap from a re-seller.
Take this opportunity to add some space, your users will love you.
John John Stoffel - Senior Staff Systems Administrator - System LSI Group Toshiba America Electronic Components, Inc. - http://www.toshiba.com/taec john.stoffel@taec.toshiba.com - 508-486-1087