<html>
<body>
At 12:48 AM 1/27/2005, Karen Shaeffer wrote:<br>
<blockquote type=cite class=cite cite="">On Sun, Jan 23, 2005 at
11:14:14PM -0800, Greg Lindahl wrote:<br>
<br><br>
These numbers are defined by their collective usage in the industry.
I<br>
accept your assertion about their definitions. But the MTBF number
has<br>
no consequential significance to a disk drive manufacturer, and
thus<br>
has a poor confidence associated with it -- and I am going to
explain<br>
why.<br>
<br>
As stated previously, the disk drive business is an extremely high<br>
volume, low margin, technology intensive business. Product cycles
last<br>
about 6 months. A typical disk drive comes out of development and<br>
ramps up from zero units to several million units within about 6
weeks.<br>
This is an operational miracle in of its self, but it is standard
buisness<br>
in this industry.<br>
</blockquote><br>
<snip of an excellent discussion><br><br>
<blockquote type=cite class=cite cite="">I and others have asserted you
cannot place much confidence in these<br>
numbers, because they have no financial consequence to the DDM.
(Except<br>
of course if they are wildly wrong -- which brings with it the
particular<br>
problem of being too late to do anything about it.) I have
explained why<br>
this is so. I have also explained how the DDM assigns all it's resouces
to<br>
the critical problems, as the rate of production is so high, time is
the<br>
essence in protecting profits. Once production ends, all resources
are<br>
reassigned to the next product to be released.<br><br>
It is my understanding that these MTBF numbers are derived from
thermal<br>
cycling in ovens as part of the QA process. All the likely failure
modes<br>
in a disk drive are quite sensitive to thermal conditions. These are
the<br>
media, the heads, the spindle, bearings, lubricants, etc comprising
the<br>
critical mechanical structure, the temperature dependence on band gaps
and<br>
other calibrating circuitry within the electronics, nominal currents
within<br>
the microeclectronics and espectially the power mosfet arrays, the
servo<br>
system cailibration, etc. As the thermal cycling QA processes
proceed,<br>
defects in these systems can be forced to manifest during the testing,
and<br>
the normal state characteristics and stability of these subsystems can
also<br>
be extracted from the experiments. These results are then
rigorously<br>
integrated within the observed profiles and characteristics of
drives<br>
failing within the infant mortality window. It is all highly
integrated<br>
within statistical models for expectations. MTBF numbers are also<br>
extrapolated from the results. In effect, the MTBF numbers become the
long<br>
term projections that are extrapolated from this data. But the
primary<br>
focus and optimization of processess is intended to create the
statistical<br>
underpinning from which to analyze infant mortality drive failures.
The<br>
uncertainty in these numbers naturally increases for the MTBF<br>
extrapolations.<br><br>
It's all perfectly logical.<br>
<br>
</blockquote><br>
I can see where this process would be typical for quick turnaround
consumer oriented drives. However, maybe there are product lines
which seem to be much longer lived.. call them "professional"
grade. Maybe they aren't really the same drive, just the same
"model name", but then, it seems that there are customers (i.e.
Defense Department, etc.) who expect to be able to buy "exactly the
same drive" for an extended period of time (several years, at
least), and that the manufacturers would accomodate them.<br><br>
If I'm making, for instance, high end video editing systems that cost a
million dollars, I'm probably not interested in saving a few bucks on the
drives, but I AM interested in drives that last a long time, and that can
be replaced easily with the same drive. (I don't build these
systems, maybe that's not their market model...)<br><br>
The fast turnaround in modern electronics is a huge curse to us
developing systems with long lead times. By the time the component
is tested and qualified (heck, even breadboarded to see if it's the
"right" component), it's obsolete and unavailable. not
just disk drives, but things like RAM, microprocessors, data converters,
RF ICs, etc.<br><br>
<br>
As far as warranties go... Here's an interesting quote from Seagate's
website:<br>
(note the identical product gets 1yr in Americas and 2yrs in EMEA
countries)<br><br>
"<br>
<b>What products are excluded from the new 5-year warranty? <br>
</b>The only products that are excluded are our retail external hard
drives (external retail products, pocket drives, portable & compact
flash drives). They are treated much more like a storage appliance and
are used in very different operating <br>
environments. We have a competitive one-year warranty on external drives
in the Americas, and a two-year warranty in the EMEA countries.<br><br>
<x-sigsep><p></x-sigsep>
James Lux, P.E.<br>
Spacecraft Radio Frequency Subsystems Group<br>
Flight Communications Systems Section<br>
Jet Propulsion Laboratory, Mail Stop 161-213<br>
4800 Oak Grove Drive<br>
Pasadena CA 91109<br>
tel: (818)354-2075<br>
fax: (818)393-6875<br>
</body>
</html>