An interesting requirement. You might like to take a look at Irmin, which is a git-like distributed storage system. It's still being actively developed but it's

An interesting requirement. You might like to take a look at Irmin, which is a git-like distributed storage system. It's still being actively developed but it's far along enough to be worth kicking the tires. http://openmirage.org/blog/introducing-irmin http://openmirage.org/blog/introducing-irmin