MTBF (mean time between failures)
MTBF (mean time between failures) is the average time a system works between one failure and the next.
MTBF comes from hardware reliability, where failures are fairly random. For software and online services failures cluster around changes, so MTBF over a quarter says more than a single figure from a datasheet.
Together with MTTR it gives availability: failing rarely and recovering quickly are two routes to the same number. Halving recovery time improves availability as much as doubling the time between failures.
At a glance
MTBF = total working time ÷ number of failures availability = MTBF ÷ (MTBF + MTTR)
Calculate availability from MTBF and MTTR →
Questions
What is the difference between MTBF and MTTF?
MTTF (mean time to failure) is for things that are replaced rather than repaired, such as a disk. MTBF is for systems that are repaired and keep running.
Is a higher MTBF always better?
It is better, but a team that ships rarely to keep MTBF high may recover slowly when something does break. Short recovery often costs less than avoiding every failure.
Related terms
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MTBF（平均故障间隔时间）
MTBF（平均故障间隔时间）是系统从一次故障恢复后，到下一次故障发生前平均正常运行的时间。
MTBF 来自硬件可靠性领域，那里的故障比较随机。软件和在线服务的故障往往集中在变更前后，所以按季度统计的 MTBF 比规格书上的单个数字更有参考价值。
结合 MTTR 就能得到可用性：少出故障和快速恢复是通往同一结果的两条路。恢复时间减半，对可用性的提升与故障间隔翻倍相同。
速览
MTBF = 总正常运行时间 ÷ 故障次数 可用性 = MTBF ÷（MTBF + MTTR）
常见问题
MTBF 和 MTTF 有什么区别？
MTTF（平均失效前时间）用于坏了就更换、不修理的东西，例如硬盘。MTBF 用于修好后继续运行的系统。
MTBF 越高越好吗？
是更好，但为了维持高 MTBF 而很少发布的团队，真出问题时恢复往往更慢。很多时候，缩短恢复时间比避免所有故障更划算。