Have a look at Open vStorage (http://www.openvstorage.com http://www.openvstorage.com). Some highlights: open-source, core is battle proven for more than 7 year

Have a look at Open vStorage (http://www.openvstorage.com http://www.openvstorage.com). Some highlights: open-source, core is battle proven for more than 7 years, performance, scales across datacenters , unlimited snapshots, ... (disclaimer: I'm an engineer there...)