4 ms·
No, because design lifetime is distinct from failure rate. Failure rate is just that: a predicted rate of failure (not lifetime) in aggregate for a model within
by jsmthrowaway 9y ago
No, because design lifetime is distinct from failure rate. Failure rate is just that: a predicted rate of failure (not lifetime) in aggregate for a model within design lifetime. Beyond lifetime, all bets are off. Think of this MTBF as saying “your two drives probably won’t fail within lifetime. A significant number of your 10,000 will.”
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.
- DamonHD 9y agoI've had a nice rack of discs, though small by today's standards, AFAIK well within any MTBF, wrecked when some junior decided to see what the phased shutdown button in the machine room did during the middle of the bank's trading day, cutting off half the power to my cabinet at one point, which SCSI doesn't protect against. There's always events dear boy, events!