Good post by Stuart Miniman (thank you) over in the Wikibon
The largest web-based companies in the world have proven a new model for managing and scaling a combined architecture of compute and storage. The hyperscale companies, such as Facebook, Google and Amazon, use a design of local distributed storage. The key differentiation of this new architecture is the ability to be extremely scalable and simple to manage. The advantages of this architecture can also benefit enterprise and service provider customers.
Read on here