How does Google Gmail store their "email" messages?

Question

How does Google store their 7GB/user emails such that it is blazing fast for retrieval and also not subject to corruption.

Is it in those NoSQL database or just jornaling file system ?

Answer 1

According to the paper "The Learning Behind Gmail Priority Inbox", Google makes "extensive use of bigtable, which combines features of a distributed file system with a database."

BigTable has been described in a 2006 OSDI paper.