COP 5611 Operating Systems Spring 2010 Dan C. Marinescu Office: HEC 439 B Office hours: M-Wd 1:00-2:00 PM

Lecture 15 Reading Assignment: Chapter 9 from the online textbook Homework 3 due today. Midterm: Wednesday March 17 Last time: Coding Replication Voting Today: Conditional reliability Repair Applying redundancy to software and data Lessons Next time Atomicity (Chapter 9) 2 2 2 2 2

Triple-redundant super-module with three voters

Reliability increases for triple-modular redundancy when mission time is short compared with MTTF

When mission time is comparable with MTTF reliability for the triple modular redundancy decreases

Effects of Replication Replication provides a dramatic improvement for missions of short duration compared with the MTTF. MTTFsystem=ln(MTTFreplica)

Failure points for a five-modular redundancy system