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Old December 19th 16, 08:51 AM posted to alt.comp.hardware
Paul[_28_]
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Default ST4000NM0035 vs ST4000NM0033

Lars Bonnesen wrote:
But with a better MTBF, I guess Seagate expect the newer ones to be more
reliable than the older ones.

Regards, Lars.


That's what the measure is intended to communicate.

Normally, you would use the MTBF as a prediction of
how many spares to stock in your stock room. I doubt
the companies running large server farms rely on
that manufacturer number, instead looking at how many failed
Seagates or WDCs they had when using the previous
model.

MTBF is more of a ceremonial dance, than a useful metric.
The manufacturer does have the information necessary to
make the number realistic. However, if they did that,
the marketing department would have the individuals
killed :-) So instead, the calculation is done in
"a standard way", devoid of the most recent field
data. That's why I object to it. There is really nothing
forcing them to be completely honest.

As long as the numbers stay in a small range, nobody
will suspect anything is wrong with the numbers.

As an example, power supplies at work, the bigger
ones are rated at 3000 FITs. And then a lab prototype
of a smaller converter, had a rating of 100 FITS. And
when someone calculates a value like that, you immediately
start grilling them with questions. But if you showed me
one unit is 3000, another 2500, then my suspicions are
not aroused. Like you, I might expect (magically)
that somehow the 2500 FIT one is better. (FIT equals
failure in 10^9 hours). When there is an extreme change
in these reliability numbers is when you become suspicious.

To give another example of dishonesty, you will notice that
some Helium drives have entered the market. And I was hoping
that the environmental spec would take a radical shift.
Instead, the specs are almost verbatim copied from
existing drives. And you know when that happens,
the marketing department said "don't scare the customers,
don't arouse suspicions". The max altitude on a sealed
Helium drive should be higher than the previous drives.
Or at least, the number should be different, not
exactly the same by chance.

I'm patiently waiting for some failure rate data
to come back from the Helium drives. By being
sealed, they should not be subject to external
moisture effects on the platters. Now, I wonder
what the MTBF figures say... Would they reflect
a difference ? Or not ?

Paul