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Security Operations · Foundational

Mean Time Between Failures (MTBF)

The average operating time between failures of a repairable system, a measure of reliability.

Definition

MTBF is calculated as total operational time divided by the number of failures. Higher MTBF indicates greater reliability. It is used with MTTR to estimate availability: Availability = MTBF / (MTBF + MTTR).

Example

A server running 10,000 hours with 4 failures has an MTBF of 2,500 hours.

Exam tip

MTBF applies to repairable items; MTTF applies to non-repairable ones.

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