Three Google engineers (Eduardo Pinheiro, Wolf-Dietrich Weber and Luiz Andre Barroso) put a report together that examined 100,000 commercial hard drives, ranging from 80GB to 400GB in capacity from a wide variety of manufacturers and models, used at Google to store cached web pages and services since 2001. The report concluded that the impact of heavy use and high temperatures on hard disk drive failure may be exaggerated: "Our data indicate a much weaker correlation between utilisation levels and failures than previous work has suggested. We expected to notice a very strong and consistent correlation between high utilisation and higher failure rates. However our results appear to paint a more complex picture. First, only very young and very old age groups appear to show the expected behaviour," the authors noted.
There is a widely held belief that heavily used hard disks are more likely to fail than those used intermittently. It has also been thought that hard drives preferred cool temperatures to hotter environments. The engineers found, however, that hard drives less than three years old and used a lot are less likely to fail than similarly aged hard drives that are used infrequently. The authors of the report speculated that drives which failed early on in their lifetime had been removed from the overall sample leaving only the older, more robust units. The report also noted that there was 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." But hard drives which are at least three years old were more likely to suffer a failure when used in warmer environments.