In simple terms, what is a "Bathtub Curve"?

Question

I think that term had been used in reference to a "Weibull Distribution". Has to do with failure rate over time of some hard drives.

Answer 1

It is a graph of failure rate versus time. Time is on the X-axis, Failure rate is on the Y-axis.

The function looks like the cross-section of a bathtub -- high at the left (where time is low), low and flat in the middle, and high at the right (after lots of time has passed).

What this indicates is that there are a lot of failures near the beginning of a product's life, called infant mortality. If one million disk drives are manufactured, there will statistically be many of them that fail when they are first turned on (or shortly thereafter). This is due mainly to manufacturing process defects (bad solder joints, improper handling causing ESD failures, etc.)

If a disk drive 'survives' the initial first few hours of operation, statistically it will survive for it's intended lifetime.

The right part of the bathtub curve shows an increase in failures. This is due to components wearing out. In the case of a disk drive; bearings wear out, seals dry out and crack, disk heads wear out , components fail, all causing the unit to fail.

.