Cloud backup and storage provider Backblaze has published its latest batch of drive reliability data. The release covers failure information for the 70,000 disks that the company uses to store some 250PB of data.

This is the first quarter that Backblaze has been using a reasonable number of new 8TB disks: 45 from HGST and 2720 from Seagate. Drives from both companies are showing comparable annualized failure rates: 3.2 percent for HGST, 3.3 percent for Seagate. While the smaller HGST drives show better reliability, with annualized failure rates below one percent for the company’s 4TB drives, the figures are typical for Seagate, which Backblaze continues to prefer over other alternatives due to Seagate’s combination of price and availability.

Annualized failure rates for all of Backblaze's drives.

Annualized failure rates for all of Backblaze’s drives.


But it’s still early days for the 8TB drives. While evidence for the phenomenon is inconclusive, hard drive reliability is widely assumed to experience a "bathtub curve" when plotting its failure rate against time: failure rates are high when the drives are new (due to "infant mortality" caused by drives that contain manufacturing defects) and when the drives reach their expected lifetime (due to the accumulated effects of wear and tear), with a period of several years of low failure rates in the middle. If the bathtub theory is correct, Backblaze’s assortment of 8TB drives should suffer fewer failures in the future.

One set of drives that doesn’t appear to be showing any signs of a bathtub curve are Backblaze’s old 2TB and 3TB HGST drives. Even with an average age of more than five years, these drives’ failure rates of 1.6 and 0.8 percent are extremely low. Backblaze is starting to retire them from its systems, not because of any reliability concerns, but simply because new 8TB disks can pack four times as much data in the same amount of rack space and with comparable power consumption.