I agree that the Carbonite upload takes forever, particularly the initial and after a photo trip, but the security offsite from my computer makes it worthwhile.I just bought WD My Book 4TB External Hard Drive Storage. Today, it will be used on a USB2 PC, and later, a USB3. After I move the images, I plan to get a Carbonite account, the one that backs up external drives. I'm guessing a new backup of an external drive with ~500GB of images, will day a few days, depending on fast Comcast's upload speed is that day(s)
I don't want to discourage you from using Carbonite, because it's a great service to have, but you should know they throttle uploads to 2-3 GB a day (at least they did when I did my initial backup). It took me months to get my computer initially backed up, and that was less than 400GB of data.