I wonder is the FBI could subpoena a critical control system say a Siemen's SCADA controller that had been hacked. If this control system were used to control a machine capable of causing grievous bodily harm or death, would the FBI not be negligent? If the FBI took a server legitimately housing an e-commerce site containing customer data, would that be considered a data breach under California law?(FTCA torts are determined under state law not under Federal)
The FTCA specifically allows claims based upon negligence to be brought against the Federal government. However, you are correct that this liability is limited by the exemption you have posted. I don't think that any reasonable person could suggest that if data were stored on a server at Google and distributed over an entire datacenter, that the entire datacenter could be seized. That exemption gives Federal employees the leeway to search a house they reasonably believe contains a fleeing suspect. It does not cover something like seizing all the cars on a block because one contained drugs. No reasonable person would suggest such a ludicrous argument in that case nor should anyone suggest that since these 100 or so servers are in close proximity in a data center they may all be seized.