Redundancy in Dependable Systems

This lecture delves into the concept of redundancy as a key technique for constructing dependable systems, complementing modularity. The instructor explains how redundancy involves duplicating components with a purpose to increase dependability, and how it is used to achieve fault tolerance, reliability, and high availability. The lecture covers the definitions of faults, errors, and failures, as well as the importance of fault models in reasoning about system failures. Various forms of redundancy, such as data redundancy and functional redundancy, are explored, along with the use of leases to prevent resource leaks. The discussion also touches on the significance of idempotency in ensuring reliable system recovery and the role of leases in guaranteeing the absence of resource leaks.

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Related concepts (4)

CS-522: Principles of computer systems

This advanced graduate course teaches the key design principles underlying successful computer and communication systems, and shows how to solve real problems with ideas, techniques, and algorithms fr

Fault tolerance

Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure, as compared to a naively designed system, in which even a small failure can cause total breakdown. Fault tolerance is particularly sought after in high-availability, mission-critical, or even life-critical systems.

Reliability engineering

Reliability engineering is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. Reliability describes the ability of a system or component to function under stated conditions for a specified period of time. Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time. The reliability function is theoretically defined as the probability of success at time t, which is denoted R(t).

Redundancy (engineering)

In engineering, redundancy is the intentional duplication of critical components or functions of a system with the goal of increasing reliability of the system, usually in the form of a backup or fail-safe, or to improve actual system performance, such as in the case of GNSS receivers, or multi-threaded computer processing. In many safety-critical systems, such as fly-by-wire and hydraulic systems in aircraft, some parts of the control system may be triplicated, which is formally termed triple modular redundancy (TMR).

Triple modular redundancy

In computing, triple modular redundancy, sometimes called triple-mode redundancy, (TMR) is a fault-tolerant form of N-modular redundancy, in which three systems perform a process and that result is processed by a majority-voting system to produce a single output. If any one of the three systems fails, the other two systems can correct and mask the fault. The TMR concept can be applied to many forms of redundancy, such as software redundancy in the form of N-version programming, and is commonly found in fault-tolerant computer systems.