Glossary · Reliability metrics
Mean time between failures
MTBF, mean time between failures, is the average time a repairable system runs between one failure and the next. The higher it is, the less often the system fails.
MTBF comes from hardware reliability engineering and counts operating time, not calendar time: the time spent down for repair is left out. For software services it is a way to say how often incidents happen.
MTBF and MTTR together set availability. A system that fails rarely but takes long to restore can have the same uptime as one that fails often and recovers in minutes; users usually prefer the second, since short outages disrupt less.
MTTF, mean time to failure, is used instead for parts that are replaced rather than repaired, such as disks.
MTBF = total operating time ÷ number of failures; availability = MTBF ÷ (MTBF + MTTR)
Example: A 30-day month (720 hours) with 3 outages totalling 1 hour: MTBF = 719 ÷ 3 ≈ 240 hours. With an MTTR of 20 minutes, availability is 240 ÷ (240 + 0.33) ≈ 99.86%.
Uptimecheck doesn’t show MTBF as a number, but its reports hold what it is made of: uptime, downtime and the number of incidents per monitor for a calendar month or the last 7, 30 or 90 days, also as CSV. The incidents page shows how many incidents the last 30 days had and the average time to resolve.
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MTTR, MTTA and MTBF measure how fast you fix incidents, how fast you respond and how often things break. Formulas, a worked example and practical ways to improve each one.
ReadMTBF is for systems that are repaired and keep running; MTTF, mean time to failure, is for parts that are replaced when they fail, such as a disk.
It means failures are rare. It says nothing about how long each one lasts, so read it together with MTTR.
Availability = MTBF ÷ (MTBF + MTTR). Doubling MTBF or halving MTTR improves availability by about the same amount.
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