"2.5 million hours MTBF"
How do they calculate that? That works out as 285 years!
Half of these drives will last 285 years of constant operation. I find that hard to believe.
How do they calculate that? That works out as 285 years!
Half of these drives will last 285 years of constant operation. I find that hard to believe.
[1] https://en.wikipedia.org/wiki/Reliability_engineering [2] https://en.wikipedia.org/wiki/Survival_analysis
Failure rate is also independent of lifetime. Drives have other measurements for lifetime.
Having 100 of this model would predict a failure about every three years (but that doesn’t mean it’d take 300 years to fail all of them). I’d be suspicious of a three year calculation, but it very well might turn out to be accurate. Remember that lifetime and failure rate are independent metrics. They’re warranted for five years, which is probably close to their predicted lifetime, and one drive of 100 failing in that time is certainly plausible.
Having 10 basically implies none of them will fail within a five-year lifetime. Again, plausible, but I think less likely.
Regarding longevity, often the predicted lifetime of a drive is close to its warranty. You will sometimes experience no issues exceeding design lifetime, and sometimes drives immediately explode. I’ve seen both, from four-year lifetime drives entering year 13 in continuous service to other drives buying the farm one day after lifetime and SMART wear indicator is fired.
As drives age, mechanical disruption becomes a much bigger deal. That rack of 13-year drives is probably one earthquake or heavy walker away from completely dead in every U. Even power loss, including from regular shutdown, will probably permanently end the drive when they’re far beyond lifetime. That’s the danger in a 24x7 server setting if you’re not monitoring SMART wear indicators (even if you are, really); power cycling your rack can, and does, trigger multiple hardware failures. All the time. If all the drives in it were from the same batch, installed at the same time, and an equal amount past lifetime, it’s very possible for the whole rack to fail when cycled — I have actually heard of this happening, once.
MTBF is unexpected failure. Design lifetime is expected failure.
There's always events dear boy, events!
MTBF lets you compare between two drives intended for a similar purpose.
For something that you own at home, the only medium that will last your lifetime in loosely controlled environmental conditions is paper.
Archival CDs might also last a lifetime (regular CDs certainly won't).
But I agree with your point that the MBTF of a single unit is not a way to predict it's lifetime.
It dawned on me when some older relatives died a few years ago that their papers, some very old, survive with a modicum of careful handling. My grandfather's immigration papers, great-grandmothers portrait on her wedding day, etc.
Today, many of us are one expired credit card away from losing all of that in digital form.
The methodology ought to be published, though.