Cloud provider Backblaze stores 75 petabytes of data across 25,000 disks. Instead of paying for specialist enterprise-class drives, it stores that mountain of data on consumer-grade hard disks – many of which are actually external drives that have been stripped of their casing – to make up for shortages following the 2011 flood in Thailand.
Realising that there's little good data available on hard disk failure rates, the company has been analysing its own collection.
It's found that the vast majority of its drives are still running after four years, with 26% failing during that time. If a drive is going to fail, it will probably do so either early on - likely because of a manufacturing defect - or after three years, a blog post from Backblaze revealed.
"For the first 18 months, the failure rate hovers around 5%; then it drops for a while, and then goes up substantially at about the three-year mark," said engineer Brian Beach. "We're not seeing that much 'infant mortality', but it does look like three years is the point where drives start wearing out."
For the first 18 months, the drive failure rate is 5.1% a year; then it falls for the next 18 months to 1.4%, before jumping to 11.8% at the three-year mark. However, Beach notes that nearly 80% of all the drives Backblaze has ever purchased are still operating.
Extrapolating from this data, Beach predicts that the median lifespan of a drive will be around six years - and this is for consumer-grade hardware used in a cloud setting.
"When Backblaze started, there were some concerns that consumer-grade disks wouldn't hold up in a data centre," Beach said. "If this six-year median lifespan is true, it means that more than half the drives will last six years, and those concerns were unfounded."
The company promised to update the stats regularly to see if the prediction holds true.
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