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Google·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Got asked one reliability/hardware question at Google, pretty short screen from what I can tell.

Questions Asked (1)

Q1

What does MTBF mean and why is it important?

System DesignTechnical Trade-offsProduct Analytics & Metrics
Author's notes

Knew the acronym (Mean Time Between Failures) but fumbled a bit explaining why it actually matters in practice.

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Suggested Approach

Start by defining MTBF clearly as Mean Time Between Failures, then explain its importance in reliability engineering and system design. Connect it to practical implications like availability, maintenance planning, and user experience, using examples relevant to software systems.

Pro tip: Mention that MTBF is often confused with MTTF (Mean Time To Failure) and that MTBF assumes repairable systems, showing depth. Also, discuss how MTBF alone can be misleading without considering MTTR (Mean Time To Repair) and availability.

1. Define MTBF

Clearly state that MTBF stands for Mean Time Between Failures, the average time between failures of a repairable system. It is calculated as total operational time divided by the number of failures.

2. Explain its importance

Discuss why MTBF matters: it indicates system reliability, helps predict downtime, informs maintenance schedules, and impacts user trust and business costs.

3. Relate to software engineering

Connect MTBF to software systems, such as server uptime, microservices reliability, or database failures. Mention how it guides design decisions like redundancy and fault tolerance.

4. Discuss limitations and related metrics

Acknowledge that MTBF is just one metric; pair it with MTTR and availability. Note that MTBF assumes a constant failure rate, which may not hold for software.

5. Provide a concrete example

Give a brief example, e.g., a service with 1000 hours total and 5 failures has MTBF of 200 hours. Explain how this informs SLOs or capacity planning.

Key Points to Mention

  • Definition: Mean Time Between Failures, average time between failures in repairable systems.
  • Calculation: Total operational time / number of failures.
  • Importance: Predicts reliability, informs maintenance, reduces downtime, improves user experience.
  • Relation to availability: Availability = MTBF / (MTBF + MTTR).
  • Distinction from MTTF: MTBF for repairable systems, MTTF for non-repairable components.
  • Software context: Used for hardware and some software reliability, but software failures may not follow constant failure rate.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.