Can I use Time Machine to back up an external USB drive in addition to my Mac's internal hard drive? Suppose I have a MacBook with a smallish SSD drive, so I attach an external USB drive to store things like my iPhoto database or iTunes folder. Can I use Time Machine to back up this external USB drive to a second external USB drive? One that already backs up the computer? I've been trying it with a USB flash drive. I've got a 1 TB external HDD backing up my MacBook's internal 500 GB drive, and I tried to make it back up the USB flash drive as well. There is plenty of space on the Time Machine drive. In Time Machine Preferences, the USB flash drive is excluded from backups, but I am able to delete it. Problem is, it becomes excluded again whenever I open the Options paneit doesn't stay excluded. So, can this be done? What am I doing wrong? Is it because it is a flash drive I'm trying to back up? Would an HDD work? Any ideas? Thanks!