http://en.wikipedia.org/wiki/MogileFS:

MogileFS was created by Danga Interactive for use with LiveJournal. It
is similar to the Andrew File System in its design goal. It is different
than a traditional filesystem in that the user has to access files via
an API. However, it's possible to implement the file system in user
space using FUSE, or a similar package.

MogileFS enables horizontal scaling of storage across any number of
machines. Files are replicated between machines according to
customizable rules such that at any time a number of drives or machines
could be lost without data becoming unavailable. It is designed for high
volume applications, such as high traffic websites, to spread storage
across cheaper machines without relying on technologies such as NFS.