Online storage is offered by many sites, but usually the data is stored centrally on a server or a server farm. Today, while surfing the net I read about Wuala. Wuala is online storage realized as a peer-to-peer network. It's not meant to increase your harddisk space, but to change the quality of the storage. It available everywhere anytime. Wuala is not open for everybody yet (invitation only) and I therefore couldn't try it.

I started thinking about how they ensure availability of files. Typical peer to peer networks are good when files are popular, i.e. when a lot of nodes download a file and offer the already downloaded parts to other  nodes at the same time. But in comparison to any soon-to-be-released blockbuster movie, which is downloaded by thousands, my data should only be available for myself and maybe some friends. That would not work obviously.

The wuala website does not tell how they ensure a sufficient availability of stored files. Just increasing the redundancy by replicating a file to a lot of nodes does not really help, because you need too many copies to get a reasonable availability level. Nodes in p2p networks are not very reliable. They come and go often. But there are much more efficient ways than simply replicating the data to add redundancy. It turns out that they in fact use the principles for forward error correction in form of Reed-Solomon codes. This youtube video about wuala has some details.

wuala is a smart idea and I hope they open it to a broader audience soon.