Quote Originally Posted by DanceswithUnix View Post
The main use of warranties is to indicate design life, because the drive companies won't give you any other figure.

I am told the MTBF is only valid for the warranty period, which is quite believable as to take an extreme case it will mean nothing in 20 years time so there must be some limit.
For an engineer, you seem to be being rather obtuse. My original point that all mechanical device break, when used, in time, still stands and is an undeniable physical fact. I did qualify that the only point to argue about is when.

The MTBF is exactly that - the mean time between failures over a very large sample of drives. It only shows AVERAGE failure rate. Any given drive can break immediately, even within warranty. That's why they give you warranty, to give you some protection for your purchase given an unfortunately quick failure. The MTBF means exactly what it means in 0 years time or 100. Just because a drive hasn't failed in 20 years when the MTBF was 10 years doesn't make the MTBF meaningless.

If a radioactive particle doesn't decay in 20 years when the half life is 10 years, does that make the half life measurement meaningless? If average life expectancy is 80 years and someone lives to 100 years, does that make the average meaningless?

The warranty is NOT "to indicate design life" - that is indeed the MTBF, which manufacturers DO give you. As stated, the warranty is purely financial protection against some drives failing from very early on, which both they and we know will happen in some cases. I'd like to see you design a HDD line that never EVER fails within a 1 year warranty period. It's impossible. So expecting that from the HDD companies is both unrealistic and unfair.