I've been reading this document which is an analysis of Google's hard
disc failure rates:

Failure Trends in a Large Disk Drive Population:
http://research.google.com/archive/disk_failures.pdf

It states that "contrary to previously reported results, we found very
little correlation between failure rates and either elevated
temperature or activity levels."

Figure 4 "shows that failures do not increase when the average
temperature increases. In fact, there is a clear trend showing that
lower temperatures are associated with higher failure rates. Only at
very high temperatures is there a slight reversal of this trend."

"Figure 5 looks at the average temperatures for different age groups.
The distributions are in sync with Figure 4 showing a mostly flat
failure rate at mid-range temperatures and a modest increase at the
low end of the temperature distribution. What stands out are the 3 and
4-year old drives, where the trend for higher failures with higher
temperature is much more constant and also more pronounced."

"Overall our experiments can confirm previously reported temperature
effects only for the high end of our temperature range and especially
for older drives. In the lower and middle temperature ranges, higher
temperatures are not associated with higher failure rates."

Figure 5 suggests that Google's optimum temperature for hard drives is
between 35C and 40C.

Elsewhere I found this old IBM article:
http://web.archive.org/web/200005192.../drivetemp.htm

It states that "figure 2 shows the dramatic effect that temperature
has on the overall reliability of a hard disk drive. Derivations [sic]
from a nominal operating temperature (assumed to be maintained over
the life of a drive) can result in a derivation [sic] from the nominal
failure rate. As the temperature exceeds the recommended level, the
failure rate increases two to three percent for every one degree rise
above it. For example, a hard disk drive running for an extended
period of time at five degrees above the recommended temperature can
experience an increase in failure rate of 10 to 15 percent. Likewise,
operating a drive below the recommended temperature can extend drive
life."

This last statement is a bit ambiguous. If a hard drive is more
reliable at a temperature below that which is recommended, then why
not recommend a lower temperature in the first place? Then again,
maybe the author's intended meaning was "recommended maximum
temperature".

- Franc Zabkar
--
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