How do I backup and external hard drive (iPhoto Library) to another external hard drive? My iPhoto Library is on an external hard drive.  I want to copy it to another hard drive as a back up.  It looks like Time Machine only backups the internal hard drive and selected externals.  I don't want to back up my internal.  I only want to backup my external.  What do i do?  What programs will do this?  If Time Machine does do this, please explain how.  I don't see that option.
Well first I would ask you: why in the world would you not want to back up your internal drive?

Second, you could easily set up Time Machine, but simply add the internal drive to the exclusions.