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Backblaze vets 8TB drives, releases updated hard drive reliability data

Backblaze has released its quarterly details on hard drive reliability, including new information on its initial deployment of 8TB hard drives. While SSDs have made marked inroads into the hard drive market thanks to a rapidly diminishing cost-per-bit, hard drives still reign supreme as the most cost-effective method of storing data.

Backblaze kicked off its 8TB migration by deploying more than 2,700 Seagate HDDs. The company migrated an estimated 6.5PB of data from a set of Storage Pods built with 2TB HGST hard drives to a set of Seagate 8TB drives, quadrupling the amount of storage available per-pod. For those of you curious about how much data Backblaze stores in total, the company has released a chart showing its own capacity growth rate over the past four years.

Early reliability data on the new drives is good, without much sign of a bathtub curve (an early period of time during which drives initially fail). Most of the drives have minimal failure rates, though there are a few cases where the gap between the low and high confidence interval is particularly large (these seem to indicate cases where Backblaze has either only recently deployed drives or has had a small number of failures in a small pool). As the 8TB drives get more use these figures should settle down. The annual failure rate of 2% across all drive families is excellent.

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Backblaze offers the following explanation for how it calculates its annualized failure rates.

Some people question the usefulness of the cumulative Annualized Failure Rate. This is usually based on the idea that drives entering or leaving during the cumulative period skew the results because they are not there for the entire period. This is one of the reasons we compute the Annualized Failure Rate using “Drive Days”. A Drive Day is only recorded if the drive is present in the system. For example, if a drive is installed on July 1st and fails on August 31st, it adds 62 drive days and 1 drive failure to the overall results. A drive can be removed from the system because it fails or perhaps it is removed from service after a migration like the 2TB HGST drives we’ve covered earlier. In either case, the drive stops adding Drive Days to the total, allowing us to compute an Annualized Failure Rate over the cumulative period based on what each of the drives contributed during that period.

Seagate continues to be Backblaze’s dominant supplier, because (and this is according to Backblaze) neither Toshiba or Western Digital is particularly interested in selling the company hard drives. This seems rather unlikely given that Toshiba and WD are in the hard drive-selling business, and may have more to do with price competitiveness. Annualized failure rates for HGST drives continue to be lower than any of the products from Toshiba, Seagate, or Western Digital, but the lower cost of Seagate hardware apparently keeps them in the driver’s seat.

Earlier this year, Backblaze released its first cumulative report on hard drive failures after logging one billion hours of drive data. As always, data presented here should be treated as indicative of drive failure rates in particular workloads and scenarios. The Backblaze data set is by far the best and most thorough data available online on how HDDs perform in the real world — but no one, including Backblaze, argues that its data is representative of all drives in all workloads, or that it can be perfectly extrapolated to other uses. Failure rates can and will vary by workload — and a certain amount of luck.

Now read: Who makes the most reliable hard drives?

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