To date, most hard drive data has been provided by manufacturers. Their tests to determine lifespan of their equipment has been accelerated, and does not necessarily reflect real world usage. Most people in the IT industry have assumed that:

• High activity levels = increased failure rates
• High temperature levels = increased failure rates
• SMART parameters provide an accurate predictor of failure

According to a study by Google, perhaps one of the world’s largest user of hard drives. These assumptions are wrong. Turns out high temp and activity are not a good predictor of hard drive failures. In reality letting your hard drives cool off is worse than letting them run a little hot. Additionally, while not a good predictor of failure in general, the following SMART parameters are a sure sign your drive is about to fail:

• scan errors
• reallocation counts
• offline reallocation counts
• probational counts

Of course, the study did explain that if you are waiting for SMART signals you may be disappointed as only a small percentage of failures were predicted by SMART. Get the full study from Google here.