On Fri, 11 Nov 2022 14:05:33 -0500 Dan Ritter <d...@randomstring.org> wrote:

> Claimed MTBF: 1 million hours. Believe it or not, this is par
> for the course for high-end disks.
> 
> 24 hours a day, 365 days a year: 8760 hours per year.
> 1000000/8760 = 114 years.
> 
> So, no: MTBF numbers must be presumed to be malicious lies.

With your interpretation every single drive would not be allowed to fail before 
its MTBF value. That's wrong. MTBF is a mean value for all drives of this type, 
not a guaranteed minimum value for a single drive. 

If there are one million drives, statistically with every hour one drive will 
fail. That means, even with correctly claiming an MTBF of 1 million hours, one 
of those million drives will statistically(!) run only one hour before it 
fails. 

Some more practical explanation: 

If you have one thousand drives then you have to expect one drive failure for 
every one thousand hours (MTBF=1,000,000). Statistically you have to expect 
nearly nine of those drives to fail per year (if I did my math correctly). With 
higher MTBF values this value will be smaller, with lower MTBF values you'd 
have to expect more drives to fail.

But this is only a pure statistical value. If you are the one of a million, 
your single drive will fail within the first hour...

(and on top there are other details, like: the MTBF is calculated for specific 
environmental conditions; if your environment is more rogue, then you'd have to 
expect a lower MTBF than the one declared by the vendor... and vice versa)

regards
hede

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