1) If a data center is using servers with 98% availability, how many of them wil
ID: 3205861 • Letter: 1
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 number of servers are required for desired relaibility
hence relaibilty with n servers =1-(1-0.98)n should be greater then 0.99999
hence 1-(0.02)n>0.99999
0.00001>(0.02)n
taking ln on both sides
-11.5129>-3.912n
n>2.94
hence required number of servers =3
2) for above analogy number of servers required by 95% rated availity server n1>(-11.5129/ln(0.05))=4
number of servers required by 99% rated availity server n2>(-11.5129/ln(0.01)) =3
as cost of 95% should be less to be competitve
hence n1*x<n2*8000
x<(3/4)*8000
x<$6000
hence that should be $2000 cheaper then its counterpart,
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