Backblaze, the low cost cloud backup and storage provider, has published its drive reliability numbers for the final quarter, and full year, of 2016.

The company uses self-built pods of 45 or 60 disks for its storage. Each pod is initially assembled with identical disks, but different pods use different sizes and models of disk, depending on age and availability. The standout finding: three 45-disk pods using 4TB Toshiba disks, and one 45-disk pod using 8TB HGST disks, went a full year without a single spindle failing. These are, respectively, more than 145 and 45 years of aggregate usage without a fault.

The Toshiba result makes for a nice comparison against the drive's spec sheet. Toshiba rates that model as having a 1-million-hour mean time to failure (MTTF). Mean time to failure (or mean time between failures, MTBF—the two measures are functionally identical for disks, with vendors using both) is an aggregate property: given a large number of disks, Toshiba says that you can expect to see one disk failure for every million hours of aggregated usage. Over 2016, those disks accumulated 1.2 million hours of usage without failing, healthily surpassing their specification.

The same model of disk has had failures in previous years. Although Backblaze's data hasn't shown much evidence of the widely-assumed "bathtub curve"—wherein disks at the very start and very end of their lives have relatively high failure rates, with a period of low failure rates in between—it's possible that a subtle bathtub effect does exist. It's also possible that an even lower failure rate will now be maintained for a few years.

For 2016 as a whole, Backblaze saw its lowest ever failure rate of 1.95 percent. Though a few models remain concerning—13.6 percent of one older model of Seagate 4TB disk failed in 2016—most are performing well. Seagate's 6TB and 8TB models, in contrast, outperform the average. Improvements to the storage pod design that reduce vibration are also likely to be at play.

In its new pods, Backblaze still tends to prefer 8TB Seagates. Traditionally, the company has stuck with consumer-oriented disks. Backblaze argues that the extra cost of "enterprise" disks doesn't make sense for its usage pattern. Backblaze is giving enterprise disks another go by adding one 60-drive pod filled with enterprise-class Seagate 8TB drives. With the consumer units already showing good reliability, the enterprise disks will have to be very good indeed to show any benefit.

After a series of upgrades and replacements, the smallest disks currently in use by Backblaze are 3TB. Over the course of the next year, the company plans to replace older storage pods using those 3TB disks with new ones. The new norm will be 8TB, especially as the firm has found that 5TB and 6TB units are becoming hard to get. This may be due to consumer preference; buyers are looking to get either the smallest disk they can reasonably get away with, in which case 1-2TB is more than adequate, or the largest disk that money can buy, in which case 8-10TB is the way to go. Mid-range drives fill neither of these roles.