Block 4 part 1

Question 1

what is the key metric availability and how do we calcul it

Answer 1

availability is the probability that an application,service,system is available to use

A= uptime ÷ (uptime + Downtime)

Question 2

Give me examples of planned downtime

Answer 2

Backup and restauration , hardware os network upgrades , application and db maintenance

Question 3

give me examples fo unplanned downtime

Answer 3

environmental factors, app errors, operator and user errors

Question 4

What is the primary cause of downtime in data centers

Answer 4

Ups system failure

Question 5

what is the average annual loss per company according to size

Answer 5

small 221 817
Medium 450 000
Large 927 823

Question 6

How do we calculate reliability

Answer 6

check slide 13
reliability is the ability for a system to perform its fucntiin ynder conditions in a specified period of time

Question 7

what is mean time tonfailure MTTF

Answer 7

measure of reliability for items that cannot be repaire
MTTF = (test period x num of item under test) ÷ num of items that fail

see example on slide 14

Question 8

what is annualised failure rate AFR

Answer 8

afr = (num of failures × 8760 hours)÷ MTTF hours × 100%

Question 9

Howbdo we calculate how much drive will fail in 1 year using AFR

Answer 9

num failures = num of drives × AFR

Question 10

What is inherent availability and how do we calcul it

Answer 10

inherent availability is the availability of a system that has not been created

Ai = MTTF ÷ (MTTF + MTTR)

mttr being the mean time to replace (time)

Question 11

what is operational availability

Answer 11

Ao = MTBM (mean time between maintenance) ÷ (MTBM + MDT (mean downtime))

Question 12

How do we increase availability

Answer 12

Load sharing -> sharing workload accross a number of computers.

the internet send a load to the load share monitor that would distribute it to multiple nodes

Question 13

What are the disadvantages of load sharing and the solutiond

Answer 13

• the monitor cannot track the responses if a node does fail
• monitor represents a single point of failure
• updates to each node independently
• no guarantee that multiple request from a client are directeed to the same node

Solution:
incorporate cookies
add a form of a shared storage

Question 14

what is heartbeat in load sharing

Answer 14

a small message that is communicated from the node tk monitor and if its not communicated the monitor will assume failure

Question 15

What is clustering

Answer 15

collection of independent computer nodes as single logicsl server to user
its goal is to increase availability

there is two form active - active (start copy of application) / active - passive (takeover in failure)

Question 16

what is fault tolerance

Answer 16

a hardware continues to operate in the event of a single hardware failure

Question 17

what are the potential benefits of virtualisation

Answer 17

• reduce cost of ownership as two virtual servers operate of on computer
• additional protection by executing untrusted app on guest os (sandboxing)
• Legacy system , emultatecolder peripherals that are no longer manufactured
• quick instalation
• quick recovery

Question 18

What is cloud computing

Answer 18

conbine high availability hardware with virtual servers

Infrastructure as a service : business with a complete set of computers

Platform as a service : business with computer platform

Software as a service : business with an entire application

does not increase availability -better utilisation of perf of processors

Question 19

what is disaster recovery

Answer 19

putting in place a plan that wil enable a company to recover its it system from a disaster - enable to functiom during a disadter

it have to describe:
what activities should be done
who should do the activitued
when and in what sequence they should be done