# Suppose we have a power supply within a system being used in a particularly harsh environment that causes it to have an MTBF of only 75,000 hours

1. Suppose we have a power supply within a system being used in a particularly harsh environment that causes it to have an MTBF of only 75,000 hours.

a. Suppose the MTTR for the power supply is 10 hours; what is the availability percentage of the component (to 3 decimal places – XX.XXX%)? Show your work!
MTBF / (MTBF + MTTR) x 100%
75,000/(75,000 + 10) x 100%=99.986%

b. Suppose that the power supply is part of a mobile, embedded system such that getting the system to a location where it could be fixed would take time, thereby increasing the MTTR for the component to 40 hours; recalculate the availability percentage (to 3 decimal places – XX.XXX%)? Show your work!
MTBF / (MTBF + MTTR) x 100%
75,000/(75,000 + 40) x 100%= 99.946%

c. What is the largest MTTR we can have for the power supply to reach “four nines” (99.990%) availability? Show your work!

2. Suppose a system consists of the components shown in the chart below, where each component has the indicated availability.

Component Availability In %
Hard Drive .99999 99.999
Power Supply .99992 99.992
Fan .99992 99.992
System Board (1) .99800 99.800
System Board (2) .99800 99.800
System Board (3) .99800 99.800
CPU .99998 99.998
NIC .99995 99.995

Be sure to show your work for a, b, and c below!

a. What is the availability percentage of the entire system (to three decimal places)?
b. Availability = (.99999 x .99992 x .99992 x .99800 x .99800 x .99800 x .99998 x .99995) = .99377
99.37 %
c. We can deploy systems in parallel to increase availability. Calculate the availability percentage we get by deploying two of the systems from answer 2a in parallel (to three decimal places).

d. Calculate the availability percentage we get by deploying three of the systems from answer 2a in parallel (to three decimal places).
= 1 – 5.12 x 10 -31 = 99.999%

3. Explain the “bathtub curve” as it relates to availability. (use your own words…do not just cut/paste the book answer!)
explain this!

4. With respect to system performance and scalability, describe horizontal and vertical scaling and give the advantages/disadvantages of each.
Vertical Scaling:
Usually refers to adding more resources to your server such as RAM and CPU. It is the most commonly used scaling method in applications and products of middle and small-sized companies and it usually means upgrade of server hardware.
pros:

cons:

Horizontal Scaling:
when a high availability of (server) horizontal scaling is a must use technology. Simply means adding more processing units to your server.

5. Name and describe the 3 steps of the Identity and Access Management security pattern.
the Identity and Access Management security pattern is the process of managing the identity of people and systems, and their permissions
1. Identification (name)
Making sure that the users or systems claim who they are
The claimed identity is checked in step 1, now in step 2 we check for