I watched a webinar a few months ago of a photographer who used to work in the database group at Microsoft... now a senior portrait and wedding photographer in the Chicago area, who stated they grossed over $1M in sales last year. He stated that, as with most photographers, he rarely needs to look over old photographs again, unless it's a previous client asking for more prints... but obviously not on a day-to-day basis. That said, he solely uses stand-alone external HDDs... and usually buys a number of them on Black Friday (when they are really cheap). One on-site for local storage, another off-site in a safe deposit box. He simply copies the files over to each drive as soon as a shoot is over. Once the off-site drive is full it goes to the safe deposit box. This way there is no RAID array, no proprietary software, or other similar failure points... and the data should be able to be accessed on any computer in the (relative) future... and no reason for him to open the computer case to deal with internal drives.
While I haven't run any tests or accounted for the costs myself, he stated that research was done and he concluded that this was the cheapest and most reliable way to access and store the data (specific for photography of coarse). That said, he also mentioned that based on the cost of the drives (again, inexpensive) he doesn't bother culling pictures and deleting pictures of the ground or other because it's just not worth the time spent doing so considering the minimal amount of disk space saved. I suppose you would need to weigh the cost of the time (hourly rate) it takes to go through and delete these pictures vs. the cost of the disk space used to store them... and also simply consider if you actually want to spend the time doing this (e.g. Could you be doing something else? Another shoot?).
Personally, I generally spend the time to do the latter anyway... For now, and the forseeable future, it's just a hobby for me, and I haven't really bothered much with even an on-site backup
However, FWIW, the majority of my pictures are on a separate HDD than my OS (Windows).