MogileFS is a open source distributed filesystem. Its properties and features include:
* No single point of failure – storage nodes, trackers, and the tracker’s databases can be run on multiple machines. A minimum of 2 machines is recommended.
* Automatic file replication – files are automatically replicated between several different storage nodes.
* Flat Namespace – Files are identified by named keys in a flat, global namespace. You can create as many namespaces as you’d like, so multiple applications with potentially conflicting keys can run on the same MogileFS installation.
* Shared-Nothing — MogileFS doesn’t depend on a pricey SAN with shared disks. Every machine maintains its own local disks.
This little beauty is an open source distributed filesystem from the author of the excellent memcached.
It features functionalities available only in very expensive commercial grids.
You can build something the size of Flickr with this.