Nowadays they use Reed–Solomon coding to effectively distribute their data without copying it to 3 places.
link here: http://static.googleusercontent.com/external_content/untrust...
actually in colossus one can tune RS coding parameters per file, to get a tradeoff between performance/durablity.
RS coding uses less copies, but same level of safety (tradeoff is the recovery computation time.)
EDIT: In this video https://vimeo.com/100153741, around the 23 minute mark