Performance Modeling and Design of Computer Systems

"Computer systems design is full of conundrums: -Given a choice between a single machine with speed s, or n machines each with speed s/n, which should we choose?
-If both the arrival rate and service rate double, will the mean response time stay the same?
-Should systems really aim to balance load, or is this a convenient myth? -If a scheduling policy favors one set of jobs, does it necessarily hurt some other jobs, or are these "conservation laws" being misinterpreted?
-Do greedy, shortest-delay, routing strategies make sense in a server farm, or is what's good for the individual disastrous for the system as a whole?
-How do high job size variability and heavy-tailed workloads affect the choice of a scheduling policy?
-How should one trade off energy and delay in designing a computer system?
-If 12 servers are