Re: USB 3.0
Update on power control: Its ugly, but a single-circuit USB-controlled unit costs $25 USD. So, 25 x $25 costs $625 USD, not the $2000 mentioned previously.
The costs mentioned in the original post were retail qty 1 on the web. I suspect you can get at least a 15% discount for this large order, so the total for each of the redundant 1PB systems is just over $50,000 USD.
Also, the architecture as stated is 7 systems, one per shelf, each capable of supporting 40 x 4TB, but actually supporting 36 to get an even balance. It might be prettier to use 8 shelves each supporting 32 x 4TB, just because it's binary. Adds slightly to the cost, but those $1200 computers are WAY overkill. In fact, since we are only powering up one set ot 10 at a time, we can actually get away with a single computer instead of 7 or 8 computers, which means we do not need the switch.
In case it's not obvious, this system is basically an automated version of a stack of unpowered disks on a shelf. Access time to a file will usually be about 10 seconds to allow the disks to spin up and stabilize.