In general, Google’s hard drive population saw a failure rate that was increasing with the age of the drive. Within the group of hard drives up to one year old, 1.7% of the devices had to be replaced due to failure. The rate jumps to 8% in year 2 and 8.6% in year 3. The failure rate levels out thereafter, but Google believes that the reliability of drives older than 4 years is influenced more by “the particular models in that vintage than by disk drive aging effects”.
Breaking out different levels of utilization, the Google study shows an interesting result. Only drives with an age of six months or younger show a decidedly higher probability of failure when put into a high activity environment. Once the drive survives its first months, the probability of failure due to high usage decreases in year 1, 2, 3 and 4 – and increases significantly in year 5. Google’s temperature research found an equally surprising result: “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,” the authors of the study found.