Backing Up To a 3rd hard drive...how??

Hi! I have a macbook and use an external hard drive (my passport) to load my photos, I use a larger drive (freeagent 500G) to back up using time machine - both are plugged in when I back up. Because I have upward of 19K photos plus music I recently purchased a Taro drive. I know in order to back up my external and computer to my 500G I need to have both plugged in and it automatically backs it up. What I have NO IDEA how to do is incorporate the 3rd drive to back up everything. Do I have to format it? Is it just a time machine preference thing? Is there a place to learn more about back up systems?
Thanks in advance for any help you guys can offer!!!!

Are you saying that you want to have 2 Time Machine backups on 2 different drives at the same time?

Or are you asking how to install a 3rd USB drive because your MacBook only has 2 USB ports?

Welcome to the Mac Forums.

As far as I'm aware, you can only use Time Machine with one external hard drive at any given time. The third hard drive can be used to back up your drive that contains the photos and music by copying the contents from the My Passport to the Taro drive. You didn't say what format the Taro drive was using? If it's already formatted to FAT-32 (likely), then you can just do a straight copy.

And by the way, many folks have lost valuable photos by not backing them up. Keeping them on only one hard drive is not a good idea. Always either back them up to an additional hard drive or burn them to DVD media.

If you need more assistance, reply back to this same thread.