When I built the latest incarnation of my Secure Server, a few years ago, I made it into a back-end, front-end system. The front end faces customers and gathers the important data, and passes it over to the back-end, which stores it. Customers don't have access to the back-end server. Also, the back-end server uses an encrypted file system. So if the back-end server is (god forbid) stolen, the thieves won't have access to the data. And if the front-end server is stolen, thieves get nothing, because the data is on the back-end.
When I built these, I thought, what if one goes down? So I built twins of the back-end and front-end; if a server goes down, I lose at most an hour's data, and I can get the spare into operation in a few minutes. And there's a fifth server, which audits the whole thing, controls the video camera that works like a CCTV, and is (yet another) backup of the data; in this case, it isn't on an encrypted file system, but it is encryped using triple-DES.
All of this was in order to comply with the PCI DSS (Payment Card Industry Data Security Standard). It's all worked very well for the last three years. And I haven't needed to use the spares.
So recently, I had a think. I don't really need the two spare servers to be powered up all the time. It's good that I have them, so I can bring them into action quickly if need be, but I don't need to keep their data up-to-date. Enter the Pi.
One Raspberry Pi, with a 400 gb hard drive (total overkill in size, it only needs about 40 gb, but you can't really get small drives now) is now being used to back up both the front-end and back-end servers (using an encrypted file system), and it's also doing the auditing and, controlling the video annd doing the (yet another) backup.
The main benefit is the reduced power consumption, but there's also the fact that one Pi with no moving parts, is replacing three computers with various moving parts (fans for example) which can now be left in a powered-off state unless needed.
And that's especially true for tomorrow. Because tomorrow, we're having a power cut. I know this because the electricity company told us.
I have a generator, but that can only supply 3000 watts, enough for maybe a dozen computers. However - the Pi uses so little power (2.5 watts) that I can run any number of them without any noticable load.
And ... today, a 64gb USB stick arrived. It's as tiny as you'd expect, but the big surprise to me was the price. £14.
At the risk of repeating something I've probably said before, my first mass storage thing was a 10 mb (that's mb, not gb) hard drive that cost £1000 and was so heavy, by the time I got it home I couldn't feel my fingers.