Comp150CPA: Clouds and Power-Aware Computing
Classroom Exercise 14
The Business Case for Clouds
Spring 2011

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In class we have explored the business case for clouds as a way of exploiting economy of scale and reassigning risks. Let's explore that in more detail.

1. In lecture, I claimed that the number of machines needed in the cloud scales (roughly) linearly with the number of clients. What determines how fast the number of machines has to grow to meet expectations?
   
   
   
   
   
   
   
   
   
   
2. I claimed that the number of staff necessary to run a cloud grows sub-linearly with the number of clients, i.e., it exhibits less than linear growth. Why does that happen?
   
3. You have 1000 employees each making an average of $60,000 a year doing data entry. What is the approximate cost to you of an hour of downtime?
   
   
   
   
   
   
   
   
   
   
   
   
   
4. At the peak sales hour of the day, about 1000 customers come to your website. Of these, about 20% buy something, and the average purchase is $20. What is the cost of an hour of downtime at the peak hour of the day?
   
   
   
   
   
   
   
   
   
   
   
   
   
   
5. (Advanced) Suppose that I have a response-time SLA that requires response within one second, and I rewrite the SLA so that it is probabilistic rather than absolute, so that it says "99% of the time, the response time should be under 1 second", and "the remaining 1% of the time, the response time should be under 10 seconds". Does this change power requirements for satisfying the SLA? Why?