04-17-2008, 01:22 PM
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| Junior Member | | Join Date: Sep 2009
Posts: 0
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 Re: Recommended hard drive temperature
Previously Franc Zabkar wrote:
> On 16 Apr 2008 22:10:18 GMT, Arno Wagner put finger
> to keyboard and composed:
>>Previously Franc Zabkar wrote:
>>> On 16 Apr 2008 12:20:06 GMT, Arno Wagner put finger
>>> to keyboard and composed:
>>
>>>>Bottom line, the Google study shows that if you can get the drives
>>>>consitently down to below 40C, temperature does not matter a lot.
>>>>So the recomendation would be to have your drives (under load,
>>>>on a hot day) below 40C at all times. Note that this also applies
>>>>to external enclosures.
>>>>
>>>>Arno
>>>
>>> AFAICS, the Google study conclusively shows that failure rates also
>>> increase when temperatures drop below 35C. In fact lower temps appear
>>> to be more dangerous than slightly higher temps, except when the drive
>>> is getting old, in which case higher temps start to become
>>> significant.
>>
>>Don't read too much into it. AFAIR they did not separate by
>>manufacturer, model and manufactuuring date. It is quite possible that
>>the drives running at lower temperatures were actually from a batch
>>that had less life expectancy from the start and stay at lower
>>temperatures because of different cooling characteristics, i.e. there
>>may well be a systematic error in the measurements.
>>
>>Arno
> The way I read it, the reliability-versus-temperature result was found
> to be consistent across all models and manufacturers.
Indeed. But did they have all models and all manufacturers
at all temperatures?
> ================================================== ================
> Failure rates are known to be highly correlated with drive models,
> manufacturers and vintages. Our results do not contradict this fact.
> For example, Figure 2 [Annualized failure rates broken down by age
> groups] changes significantly when we normalize failure rates per each
> drive model. Most age-related results are impacted by drive vintages.
> However, in this paper, we do not show a breakdown of drives per
> manufacturer, model, or vintage due to the proprietary nature of these
> data.
> Interestingly, this does not change our conclusions. In contrast to
> age-related results, we note that all results shown in the rest of the
> paper are not affected significantly by the population mix.
> ================================================== ================
> The data in this study are collected from a large number of disk
> drives, deployed in several types of systems across all of Google’s
> services. More than one hundred thousand disk drives were used for all
> the results presented here. The disks are a combination of serial and
> parallel ATA consumer-grade hard disk drives, ranging in speed from
> 5400 to 7200 rpm, and in size from 80 to 400 GB. All units in this
> study were put into production in or after 2001. The population
> contains several models from many of the largest disk drive
> manufacturers and from at least nine different models.
> ================================================== ================
Hmm, I have to look at the paper again. This smells rather
strongly of a methodical error.
Ok, I have it now. I think you refer to figure 5: "AFR for average
drove Temperature". This one seems to indicate slightly higher failure
rates for the 15...30C window than for the others in drives younger
than 3 years. If you consult figure 4, you see that temperature
extremes are rare. Then there is one thing: Partially defective drives
work slower or not at all. This may result in lower drive temperatures
(spin down, refusal to execute access) and higher drive temperatures
(lots and lots of retries, heat from bearings). This can
significantly skew the results. The basic results could be that
failing drives run hotter or colder than others. I am also missing
more break-downs into different temperature profiles (e.g. mainly
constant, strong variation, etc..) as it is, e.g., possible thet the
problem in the low temp section is due to cycling temperatures.
I am not saying the results are wrong, but they are suspicuous and
with the data given are _very_ difficult to even understand
properly. It does not seem any statistics expert was consulted by the
writers and the temperature results are by far the weakest in the
paper. I also miss a proof or at least conclusive argument that the
remaining observations are temperature independent, both for absolute
value and different change profiles.
The paper is still very valuable. Figures 7-10 give solid results, and
need no further details. Scanning your disks every 2 weeks or so and
monitoring reallocation counts is a very good idea (and something I
have been doing for several years now). The folks at Google likely
also found that the SMART status alone is typically over-optimistic.
As to many failures not being predicted by SMART data, my results
are different. It is possible that the drive selection here again
skewed the picture compared to modern drives. Personally I have had
100% prediction by SMART attributes (not SMART status though) in
an addmittedly small population of about 50 drives over three
years and with mostly Maxtors that are known to fail gradually.
Arno
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