Well, I'm always discovering packages for linux I didn't know existed. This is most of the way there, though in the vision articulated it also runs on other OSs (indeed, many people don't have 3 or 4 linux boxes but do have extra windows boxes.) And I had the idea that it could be shared and efficient for all the machines hosting it. Ie. in the example above with 2 machines with 2 disks each, one is the host and the other the client, and if the client wants to write a block, he has to send it to the host, which then sends the distributed blocks back to the client, and likewise for read. Ideally you want a system where you know which blocks are local and which are remote.

Probably need a central server to maintain the actual filesystem cohesion though with a bit of work you could minimize the network traffic on that.

Also, as fully visualized, in a RAID-5 with one disk per machine and 3 or more machines, you want it so that any machine can be taken down. That requires a truly peer based system.