6.033 Spring 2005: Preparation for Recitation 15

Read sections D and E, and appendices A and B of chapter 8.

Review Section D, which presents techniques that show up in almost every fault-tolerant system design. Section D shows that the MTTF of a single-engine plane is better than that of a 3-engine plane. What does that mean for a proposal to send three Mars rovers out to do three copies of the same experiment?

Appendix A reports on a number of fault-tolerant systems that failed to meet their goals, even though the designers had the best intentions. Appendix A is light-weight reading but highly informative. Identify principles from section E.1 that were violated in "Advantures with error correction."

Appendix B presents a sequence of nonvolatile storage designs with increasing reliability. Give one example of:

• a failure that fail-fast storage can tolerate but raw storage cannot.
• a failure that stable storage can tolerate but fail-fast storage cannot.

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