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.