I can't offer any insights into other clustering FS solutions, but I think it's a very safe bet to say that Google relies entirely on GFS for their long-term storage. Granted, they almost certainly make offline backups of business-critical data, but I would assume that everything related to GMail, Google Code, Picasa, Google Docs, etc. is stored in, and only in, one or more massive GFS clusters. Take for instance their pride in the fact that they (claim) to have lost only one 64MB block in the history of their modern infrastructure (that is, since 2004).
Look at it another way: how would you backup petabytes of data? When you've got multiple data centers consisting of thousands of nodes, and every data block is replicated on at least three machines, what's the point of backups? Again, I'm no expert, I'm just basing this on everything I've read and watched about Google. Hopefully others will have more enlightened comments. n
