A responsible cost and revenue analysis is crucial in any design process. Let Cp represent the annual personnel cost to the data center for each person on the repair staff. Let Cm represent the annual cost to the data center per machine. This cost includes annual hardware and software costs, software licenses, rental/lease space per machine, energy expenses/machine, and data center fixed costs pro-rated per machine. Thus, the total annual cost to the data center, Ca, is represented by
Let Ra be the annual revenue, represented by the expression
where b > 0 is a constant revenue multiplier, No is the average number of machines in operation, and Mmin is the minimum number of machines that need to be in operation for the data center not to have to pay a penalty (indicated by a negative revenue) to its customers.
The annual profit P of the data center is the difference between the revenue and cost. Hence,
The following values are used to generate the profit graph shown in Fig. 7.6: M = 120, l = 0.002/min,m = 0.05/min, Mmin = 10, Cp = $100,000, Cm = $40,000, and b = $100,000. The curve indicates that for low numbers of service personnel (i.e., N 2) the profit is negative because of low machine availability, implying penalties being paid to the customer. With additional personnel (i.e., No of operational (i.e., revenue generating) machines.
Figure 7.6. Annual profit vs. number of repair personnel for the data center.