1) If a data center is using servers with 98% availability, how many of them wil

Question

1) If a data center is using servers with 98% availability, how many of them will be needed to provide an infrastructure that is available 99.999% of the time? Justify your answer (show math).

2) Given the choice between using servers that have 95% rated availability and servers that have 99% rated availability, if the 99% servers cost $8,000 each, how much cheaper would the 95% servers have to be to make it worthwhile to justify using them in a “five 9’s” environment. Justify your answer (show math involved and explain reasoning).

Explanation / Answer

let n be the nuber of data servers.

hence total system relaibility =1-(1-0.98)n

hence that they will be available 99.999% of the time 0.99999<1-(1-0.98)n

(1-0.98)n <0.00001

n>2.94

hence n=3

2) for 99% rated servers, number of servers reuired n1 from above analogy n=3

for 95% rated servers, number of servers reuired n1 from above analogy n =4

let cost of 95% rated server is x

hence for total savings to be positive

4x<3*8000

x<6000

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