first off, everyone who's using p2p wants it for free. you'll never make any money trying to sell this.

second, why not just buy an external hard drive. i bought a 200GB USB2 drive for $100. i also periodically backup to dvd-rw. i can fit 3+ gig on a single sided dvd, and 650 mb on a cd-rw. why would i want to give up 1 gig of my hard drive to backup 50 mb?

speed will also be an issue. if only one peer has your data, it'll take forever.

if you buy one more external hard drive, it still can fire in the flame together with your first one. it isn't a question of your disk's space amount - it is about your information safety.
You can charge money for using this service. you also may egt money from ADs.

yours, Alex

I understand the idea, you give up a certain amount of hard drive space on your own machine to in turn, allowing you to mirror a certain amount of data of your own.

you have already explained that yes there would have to be a certain amount of redundancy, and you could create hashes to be able to recover all your data if only 80% of the original file is available.

While I would point out something extremely similar has already been done by a product called folder share (recently acquired by Microsoft) which was created to share files from certain folders with other people, or with yourself.

The biggest flaw to this in my mind is the resource cost of running such a program, Bit torrent style P2P sharing is not cheap when it comes to cpu cycles and network load. Granted Bit torrent was built for speed of delivery, not economy of resources, but I like anything that is sitting in the background to be low key and consume as little resources as possible. Plus, how are you going to make money by doing this?

In my mind, the better idea would be to create a company online who specializes in backing up your data to them, upon recovery, you can either download your files, or have them ship you a burned hard copy, if it is too big.