I worked on the design of Dropbox's exabyte-scale storage system, and from that experience I can say that these numbers are all extremely optimistic, even with their "you can do it cheaper if you only target 95% uptime" caveat. Networking is much more expensive, labor is much more expensive, space is much more expensive, depreciation is faster than they say, etc etc. I don't think the authors have ever done any actual hardware provisioning before.
I didn't read all their math but I expect their final result to be off by a factor of 2-5x. Hard drives are a surprisingly low percentage of the cost of a storage system.
I didn't read all their math but I expect their final result to be off by a factor of 2-5x. Hard drives are a surprisingly low percentage of the cost of a storage system.