Interesting, I was just reading a similar article on Wired; this quote caught my eye...

Over the last several years, as Facebook expanded its online empire to hundreds of millions of people, company engineers came to realize they needed a new way of building this empire. They couldn’t use traditional hardware from traditional suppliers like Dell, HP, and Cisco. It was too expensive, too elaborate, and too difficult to operate at such an enormous scale.

So, they built a cheaper, more streamlined, and more malleable breed of gear, including computer servers, data storage devices, and networking switches. The basic idea was to build very large networks from very small and very cheap pieces that could be easily reprogrammed—and easily replaced.