Time Machine advertises itself as able to backup external hard drives, which is exactly what I need because I store all my raw pictures and video on an external hard drive. However, after plugging in my external, Time Machine never picked it up. Turns out that that external hard drive needs to be formatted as “Mac OS Extended (Journaled)”. I think I’d formatted it initially as NTFS.. i don’t remember. Sooo, luckily I have enough hard drive space to copy all the data from my external to my laptop, format the external, then copy everything back. It’s a little bit of a pain in the ass, but it’s all in the name of keeping these pictures and videos secure.