I have an iMac and MBA and 1 external hard drive and use Time Machine on both machines. I always have my external hard drive hooked up to my iMac and use Time Machine on it...and plug the external hard drive into the Air whenever I want to back it up...they're partitioned so now worries...but I noticed that my Air is Time Machine backing up on my SSD. I want the 8GB of backup on my Air erased...I still have everything on my external hard drive so I don't need it on my SSD. How do I erase these 8GB of backups? And how do I stop Time Machine from backing up to my SSD?