Slow RAID for the home network
Hard disk drives these days are cheap. Too cheap, in that while we love paying 30 cents/GB, the reliability is getting pretty poor. Doing backups, especially automatic backups is a must, but what about RAID?
One of the problems with RAID, at least RAID-5 is that you need to have 3, and ideally 4 or 5 drives in a machine. That's a lot of drives, a lot of power, a lot of heat, a lot of noise. And many machines only have two IDE controllers so they can barely do 3 drives and can't readily do more even if they had the slots and power for them.
So I propose a software RAID-5, done over a LAN with 3 to 5 drives scattered over several machines on the LAN.
Slow as hell, of course, having to read and write your data out over the LAN even at 100mbits. Gigabit would obviously be better. But what is it we have that's taking up all this disk space -- it's video, music and photos. Things which, if just being played back, don't need to be accessed very fast. If you're not editing video or music, in particular, you can handle having it on a very slow device. (Photos are a bigger issue, as they do sometimes need fast access when building thumbnails etc.)
This could even be done among neighbours over 802.11g, with suitable encryption. In theory.
Not that there aren't some major issues to overcome. The machines must be on most of the time. (A single disk can be taken out of a RAID temporarily, and thus a single machine hosting one disk can be turned off or rebooted, but not for long periods.) If you lose access to two disks (or your LAN) you can't get access to the data. And it's going to use a lot of your network capacity, though gigabit networking is starting to get cheap. And the idea gets better... This is actually more relaible than RAID in a single machine. Common errors that RAID can't fix include fires, bad power supplies that fry all the drives, certain types of power spikes, overheating of the entire case etc. In these cases you lose all the drives in your RAID. The software RAID I propose could get you through these, even a limited fire. Though offsite backup is still your best bet.
You could even RAID over the internet, which is OK for music, though would be pushing it for video.
Of course it's all software. You decide on the size of the RAID block, and everybody allocates a file or partition of that size on their system, or more than one of them if desired. For example, 2 machines might do well with a 4-disk RAID, 2 in each system, though this would not protect you from system loss the way 4 independent systems would. You would use regular, non-RAID (or Raid-1) for the working parts of the filesystem (OS, etc.) and use traditional offsite backup for it. Each computer (which could be running any OS) would hae a driver to talk to the net and make things happen. The system could make a big pool of space or give everybody a personal space equal to 2/3 to 4/5ths of the space they offered. And of course, you must be ready if a drive or system fails, to swap it out and rebuild. Rebuild will suck up the network.