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Official Google Enterprise Blog: Bringing it all together for Google Apps customers: 30GB shared between Drive and Gmail

Life gets a bit easier when your Google Apps products work well together -- whether that's inserting a Drive file into an email or sharing Docs and photos from Drive on Google+. As that experience becomes seamless, having separate storage doesn't make as much sense anymore.

http://googleenterprise.blogspot.fr/2013/05/bringing-it-all-together-for-google.html