Backblaze, a cloud storage supplier, has just updated its January report on hard disk drive reliability, and the bad news is that 3TB drives are failing faster than expected. Compared with January (reported here), the failure rate of Seagate 3TB drives has climbed from 9 percent to 15 percent, while the failure rate of Western Digital 3TB drives has jumped from 4 percent to 7 percent. As the chart below shows, only the more expensive Hitachi Deskstars — a brand that started life at IBM - have shown an improvement. The September findings are based on Backblaze's use of 34,881 drives storing more than 100 petabytes of data.

All the drives are "consumer grade" rather than "enterprise" drives, because enterprise drives are more than twice the price. Backblaze says: "Even if there were no warranty, a 15 percent annual failure rate on the consumer 'desktop' drive and a 0 percent failure rate on the 'enterprise' drive, the breakeven would be 10 years, which is longer than we expect to even run the drives for."

Backblaze's numbers are useful because it's buying drives in larger volumes than most companies, and tracking their performance more closely. And while other cloud storage companies are no doubt doing the same thing, they're not sharing their results. The three least reliable drives tested are all Seagate Barracuda models. The Seagate Barracuda 7200.11 has had an annual failure rate of 24.9 percent, the 3TB 7200.14 of 15.7 percent, and the 1.5TB Barracuda LP of 9.6 percent. However, the 1.5TB drives are relatively old — their average age is 4.3 years - and the failure rate of hard drives increases with age.

The 3TB Western Digital Red hard drive is doing badly with a failure rate of 8.8 percent on what are basically new drives: the average age is only 6 months. By contrast, the failure rate on Backblaze's 3TB Hitachi Deskstar 5K3000 drives, which have an average age of 2.1 years, is only 0.7 percent.