Compute mean time between failures for a device or a serial chain of devices, with the failure rate and annual failure count.
MTBF is an aggregate rate, so it is measured across the whole fleet rather than one box. Devices in series are less reliable than any individual member because their failure rates sum — five devices each with a 100,000-hour MTBF give a path MTBF of 20,000 hours. Every extra inline device — a firewall, a WAN optimiser, a tap — measurably lowers path reliability, and MTBF is how you quantify that before adding it.
Network MTBF
MTBF = (device-hours of operation) ÷ failures; for devices in series the failure rates add, so MTBF_path = 1 ÷ Σ(1 ÷ MTBF).
MTBF = (device-hours of operation) ÷ failures; for devices in series the failure rates add, so MTBF_path = 1 ÷ Σ(1 ÷ MTBF). MTBF is an aggregate rate, so it is measured across the whole fleet rather than one box. Devices in series are less reliable than any individual member because their failure rates sum — five devices each with a 100,000-hour MTBF give a path MTBF of 20,000 hours.
Every extra inline device — a firewall, a WAN optimiser, a tap — measurably lowers path reliability, and MTBF is how you quantify that before adding it.
This calculator takes 4 inputs: Observation period, Failures observed, Devices in the observation, Devices in series on the path. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.