One of the challenges to modern photogs, is where to put all the media. Image quality increases every year and there is a reciprocating increase in the size of your data. For the casual shooter the computer's on board drive is sufficient. Even SSD are becoming prevalent in sizes greater than 500GB. However if you are a serious photog you know that extra space is a valuable resource.
If you shoot RAW or video it is even tougher to have enough. And then backup? What? Waste a drive on copies? Yes. But it gets worse. I am here to say that backup AND redundancy are a requirement to any photographer who is ever going to be paid. There are backup solutions online. And those are great for home use. But you need on site redundancy and onsite backup. Like so:
Photog takes picture ----> Picture goes to production PC ----> Picture is reviewed/ edited(depending on your workflow) ----> Picture is placed on external NAS box with at least RAID1 but better RAID5 for redundancy(You can skip this step if you store your pics on a workstation w/RAID) ---->The NAS is then backed up to an external drive(My external drive is another RAID1 NAS, but that is probably overkill). ---->The picture is then deleted off the camera.