Re: Using two external hard drives, how do I sync my "Photos" so that my edit update on both drives?
I have 2 terabytes of storage on iCloud just so I won't have to keep up with external drives. I'm not sure you're going to find a solution, if any, that's not worth the aggravation and frustration of keeping multiple hard drives updated. Wjile I do use external drives, if they are not synched to my online drives regularly it's not the end of the world.
However, I see the point of "you don't always have cellular service, what if you need a file on your iCloud drive?".