1. FAULT-TOLERANT COMPUTING
2017/4/22
FAULT-TOLERANT COMPUTING
Jenn-Wei Lin
Department of Computer Science and Information Engineering
Fu Jen Catholic University
Motivation and Introduction
Lecture Set 1

2. ECE 753 Fault Tolerant Computing
2017/4/22
General Information
Textbook
Marin L. Shooman: Reliability of Computer Systems and Networks: Fault Tolerance, Analysis, and Design, John Wiley and Sons, 2002.
D.P. Siewiorek and R.S. Swarz: Reliable Computer Systems: Design and Evaluation, 3rd ed. A. K. Peters, 1999.
D. K. Pradhan, editor, Fault-Tolerant Computer System Design, Prentice-Hall, The book is out of print
Paper
Dependable Computing Conference
Grading Policy
Exam. 20%
Presentation 40% (four)
Term report & Project 40%
Do not discuss much about topics here.
Under computer system
overall implies what is a compute system - its architecture and
components
Then focus on hardware and software components
ECE 753 Fault Tolerant Computing

3. ECE 753 Fault Tolerant Computing
2017/4/22
Overview
Motivation
Introduction
Terminology
Fundamental Principles
Fault-Error-Failure concept
Do not discuss much about topics here.
Under computer system
overall implies what is a compute system - its architecture and
components
Then focus on hardware and software components
ECE 753 Fault Tolerant Computing

4. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation
Informal Definition
Key Attributes
Who, What and Why Study
Examples
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

5. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation
What is Fault-Tolerance?
A “fault-tolerant system” is one that continues to perform at desired level of service in spite of failurs in some componetns that constitute the system.
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

6. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation (contd.)
Who is concerned about fault-tolerance?
System Users
Who is concerned at design stages?
Universities
R, d, and a (Research, development, applications)
Industry
r, D, and A (research, Development, Applications)
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

7. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation (contd.)
Examples
General Purpose Systems
PCs: RAMs with parity checks
Workstations: error detection (HW), occasional corrective action (SW), ECC (HW), keeping log (SW)
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

8. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation (contd.)
Examples
Reliable Systems
Telephone systems
Banking systems e.g. ATM
Stock market
Football games display/ticketing
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

9. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation (contd.)
Examples
Critical and Life Critical Systems
Manned and unmanned space borne systems
Aircraft control systems
Nuclear reactor control systems
Life support systems
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

10. ECE 753 Fault Tolerant Computing
2017/4/22
Motivation (contd.)
Examples
Reliable -> Critical Systems
911 telephone switching system
Traffic light control system
Automobile control system (ABS, Fuel injection system)
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

11. ECE 753 Fault Tolerant Computing
2017/4/22
Introduction
Historical perspective and major push
Goals of fault-tolerance
Applications of fault-tolerance
Do not discuss much about topics here.
Under computer system
overall implies what is a compute system - its architecture and
components
Then focus on hardware and software components
ECE 753 Fault Tolerant Computing

12. ECE 753 Fault Tolerant Computing
2017/4/22
Introduction (contd.)
Historical Perspective
not a new concept
first use by J. van Neumann 1956
Major push
Space program
HW Fault tolerance - then
SW Fault tolerance later
Merge the two
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

13. ECE 753 Fault Tolerant Computing
2017/4/22
Introduction (contd.)
Applications
Space borne system
long life system
Airplane control system
critical system
Transaction processing system
high availability system
Switching system
high availability over certain level of performance
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

14. ECE 753 Fault Tolerant Computing
2017/4/22
Terminology
Reliability and concept of probability
R(t): conditional probability that a system provides continuous proper service in the interval [0,t] given that it provided desired service at time 0.
Availability
The probability that an item is up at any point in time
Uptime/(Uptime+Downtime)
Dependability
Property of computer system that allows reliance to be placed justifiably on service it delivers
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

15. Fundamental Principles
Dependability
Impairments
Faults, errors, failures
Means
Fault Avoidance, Fault Tolerance, Fault Removal, Fault Forecasting
Measures
Reliability, Availability, Maintainability
ECE 753 Fault Tolerant Computing

16. Fundamental Principles (contd.)
A set of methods, tools and solutions that enable development of dependable systems.
- Fault Prevention: how to prevent fault occurrence or introduction,
- Fault Tolerance: how to ensure a service up to fulfilling the system’s function in the presence of faults,
- Fault Removal: how to reduce the presence (number seriousness) of faults,
- Fault Forecasting: how to estimate the present number, the future incidence, and the consequences of faults
ECE 753 Fault Tolerant Computing

17. Fundamental Principles (contd.)
Fault Avoidance: To prevent by construction fault occurrence. E.g., nearly fault-free components, shielding against electromagnetic fields
Drawbacks:
- Cost of near-perfect components high
- Cost of maintenance personnel
Fault Tolerance: To provide, by redundancy, service complying with specification in spite of faults occurring
ECE 753 Fault Tolerant Computing

18. Fundamental Principles (contd.)
Fault Removal: To minimize, by verification, the presence of faults. E.g. Am I building the right system? Concepts of coverage,etc.
Fault Forecasting: To estimate, by evaluation, the presence, occurrence and consequences of faults. E.g. For how long will the system be right ?
ECE 753 Fault Tolerant Computing

19. Fundamental Principles (contd.)
Reliability: A measure of continuous delivery of proper service (or equivalently, of the time to failure) from a reference initial time
Availability: A measure of the delivery of the proper service with respect to the alternation of delivery of proper and improper service
Maintainability: A measure of continuous delivery of improper service (time to restoration or repair)
ECE 753 Fault Tolerant Computing

20. Fundamental Principles (contd.)
2017/4/22
Fundamental Principles (contd.)
Hardware redundancy
Low level
High level
Software Redundancy
Time Redundancy
Information Redundancy
Do not discuss much about topics here.
Under computer system
overall implies what is a compute system - its architecture and
components
Then focus on hardware and software components
ECE 753 Fault Tolerant Computing

21. Fundamental Principles (contd.)
2017/4/22
Fundamental Principles (contd.)
Hardware Redundancy - Low level
logic level
Example 1 - Self checking circuits
Example 2 - Arithmetic code
A modular adder using the mathematical principle
(A+B+|) mod k = ((A mod k) + (B mod k)) mod k
Hardware Redundancy - High level
Triplicate or 5-copies as in space shuttle
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

22. Fundamental Principles (contd.)
2017/4/22
Fundamental Principles (contd.)
Software Redundancy
Use two different programs/algorithms
Time Redundancy
Re-compute or redo the task and compare the results
May or may not use the same hardware/software
Information Redundancy
backup information
Use of ECC
Question - What kind of FT is achieved?
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

23. Fault-Error-Failure concept
2017/4/22
Fault-Error-Failure concept
Intuitive definitions
Origins of faults
Methods to break FEF chain
Attribute of faults
Do not discuss much about topics here.
Under computer system
overall implies what is a compute system - its architecture and
components
Then focus on hardware and software components
ECE 753 Fault Tolerant Computing

24. Fault-Error-Failure concept (contd.)
2017/4/22
Fault-Error-Failure concept (contd.)
Intuitive definitions
Fault -
An anomalous physical condition caused by a manufacturing problem, fatigue, external disturbance (intentional or un-intentional), desgin flaw, …
Causes
Error - Effect of activation of a fault
Failure - over-all system effect of an error
Fault -> Error -> Failure
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

25. Fault-Error-Failure concept (contd.)
2017/4/22
Fault-Error-Failure concept (contd.)
Failure occurs when the delivered service deviates from the specified service; failures are caused by errors
Error is the manifestation of a fault within a program or data structure
Fault is an incorrect state of hardware or software resulting from failures of components, physical interferences from the environment, operator error or incorrect design
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

26. Fault-Error-Failure concept (contd.)
2017/4/22
Fault-Error-Failure concept (contd.)
Causes of faults
Specification mistakes
Incorrect algorithms, architectures, or hardware and software design specification
Implementation mistakes
Process of transforming hardware and software specifications into the physical hardware and the actual software
Poor design, poor component selection, poor construction, software coding mistakes
Component defects
Manufacturing imperfections, random device defects, and component wear-out
External disturbance
Radiation, electromagnetic interference, operator mistakes, battle damage, and environmental extremes
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing

27. Fault-Error-Failure concept (contd.)
2017/4/22
Fault-Error-Failure concept (contd.)
Causes of faults
Specification
Mistakes
Software
Faults
Implementaion
Mistakes
Errors
System
Failures
External
Disturbances
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
Haredware
Faults
Component
Defects
ECE 753 Fault Tolerant Computing

28. Fault-Error-Failure concept (contd.)
2017/4/22
Fault-Error-Failure concept (contd.)
Characteristics of faults
Fault nature
Specify the type of fault
Is the fault a hardware or a software fault?
Fault duration
Specify the length of time that a fault is active
Permanent fault
Transient fault
Appear and disappear within a very short period of time
Intermittent fault
Appear, disappear, and reappear repeatedly
Fault extent
Fault is localized to a given hardware or software module or globally affects the hardware, the software, or both.
Fault value
Determinate or indeterminate
Fault sensitive to either the data or time
Be sure everyone has a conduct sheet.
Re GROUND RULES:
1. In terms of allowed collaboration vs. individual work, ask if you are not sure.
2. Deactivate all cell phones or pagers during class unless you are on-call during your job.
3. No tape-recording permitted. Take notes.
ECE 753 Fault Tolerant Computing