Question $4$: $(20$ marks$)$

A data centre power system has $3$ potential power supplies to its server rooms. The original

design provided $300\%$ redundancy sufficient for power supply i$.$e$.$ one supply whether from

the ESB or its own backup generators alone was sufficient to power the server rooms. The

probability that a power supply was functional $($non$-$failed$)$ in the event of a power outage is

$95\%.$

Additional equipment has been added to the server room. It has been calculated that now $2$

out of the $3$ supplies is now required to power the servers.

$($a$)$ Draw the block diagram for both scenarios as described in the question.

$(5$marks$)$

$($b$)$ Calculate the original reliability and then the impact on reliability of the new

arrangement?

$(15$marks$)$