What happens if external hard drives serving the primary photos library gets filled? How do I ensure my photos in the current hard drive remain intact and I can continue storing photos in the next unfilled hard drive later?
Like any hard drive, if it gets filled, you will not be able to put any more data on it until you make room for it. With that being said, if you know you’re getting close to capacity, stop saving photos to it. As for insuring your pics are safe, there are NO guarantees so you should have at least one other backup somewhere.