As for physical attacks, Google is ultra paranoid about physical access to DCs, and I think we can quickly agree that rogue employees and outsiders would have little chance of successful attack given the outrageous (and secret) methods that Google employs. Remember, this is one of the most-attacked organizations in the world, they've had decades (plural) to enact defenses and test them, and a successful attack would cost them over $10 billion - there's a virtually unlimited budget for physical defense. Circa 2020, I'd put Google's physical intrusion defenses up against most military installations.