Information Week has an interesting article, Google Revealed: The IT Strategy that makes it work. It includes interesting side bar articles as well.
“Google has between 200,000 and 450,000 servers spread among up to 65 data centers, depending on how you define them and who's doing the counting. And those numbers continue to rise.”
“Google organizes its machines, which run Linux, into ‘cells,’ which DiBona describes as a kind of disk drive for Internet services. (Not to be confused with Gdrive, the long-rumored Google hosted storage service. ‘There is no Gdrive,’ a spokeswoman insists.) Software programs reside on racks of inexpensive computers, and programmers decide how much redundancy to give them. The cells take the place of commercial storage equipment; DiBona says Google's cells are cheaper to create and maintain, and he hints they can handle more data, too.”
(The underline/bold is mine).