The Founding Principle

At the heart of PeerStorage is a system that stores data reliably on devices that keep going offline. Here is an illustration of one way to build a virtual block device from many separate devices, each contributing a share of its own memory.

Each square is a “data store”. It is made of:

• Grey cells, which hold data bits.
• Coloured cells, which hold parity bits.

Try it yourself to see how it works:

• Click grey cells to flip data bits. Watch how the parity bits change as well.
• Click coloured cells to destroy a “store”. Watch how the data is rebuilt from the rest.
• Change values while a “store” is rebuilding. Notice that your changes are taken into account.
• Destroy more than one “store” at a time. If bits are lost they are shown as “-”.

Experiment with different sizes. Watch how the redundancy ratio changes (total cells / grey cells).

A simple probability calculation under these assumptions:

• we move to three dimensions instead of the two used in the demo,
• the side of the “cube” is 11 “data stores”, so there are 1,331 in total,
• the redundancy ratio is 1.33, i.e. 1,331 / 1,000,
• every minute, 10% of the “data stores” disconnect,
• it takes 5 seconds to rebuild a “data store”.

Over a year, the probability of losing data is one in ten million (10^-7).