If you aren’t using Backblaze, you should absolutely try GoodSync. For those of you who back up your collection to Amazon Prime, it’s an absolute must-have tool. It keeps track of which photos have been changed or uploaded and only uploads the ones that aren’t already there. It will allow you to create more than one back up too so you can back up to Amazon (among MANY others) and your local external hard drive backup (a fundamental principal of the 3-2-1 backup strategy.) And, you can set up scheduled back ups so you never have to remember if you backed up or not.
This is one piece of software we can’t do without. It also works with PC, Mac and even Linux!