Last Fall when we went to Sun for an executive briefing, I fell in love with their Sun Fire X4500 ("Thumper"). I joked that I wanted one for home.
Now Data Robotics has an equivalent for the home market. The underlying technology is obviously different than Sun's Thumper but the result is similar.
It's a 4-bay SATA enclosure with USB 2.0 attachment. You just stick in a couple of drives and it figures out the best way to protect as much storage as possible. There's a good illustration of how it uses a mixture of RAID and mirroring in George Ou's blog post below.
If you need more space, add another drive or just pull out the smallest drive and stick in a larger one. Oh, don't worry about moving your data off before you do this. Just yank it out with the Drobo running.
With 2 400GB drives, I get 371GB protected. If I add another 400GB drive, I go to 743GB! Don't you love RAID? (Ok, pseudo-RAID)
Here's a couple of blog posts that give a lot more details.
But, it is a .NET 2.0 application. While the Drobo Dashboard was a 17MB download, the .NET Framework was a 23MB download. And now I have 3 Windows security patches to apply!