Who makes the most reliable hard drives?

A few months ago we asked and answered one of computing’s oldest questions: How long do hard drives actually last? That story missed one vital piece of information, though — who makes the most reliable hard drives? Well, we can now answer that question too.
Just like last time, this information comes from Backblaze, an all-you-can-eat online backup company. Backblaze currently has around 28,000 hard drives powered up and constantly spinning, storing a total of around 80,000 terabytes (80 petabytes) of user data. As you can imagine, it is very much in Backblaze’s interests to ensure that it buys reliable hard drives. Every time a drive fails, it takes considerable time and effort to pull the drive, slot in a new one, and rebuild the RAID array.

Which hard drive manufacturer is the most reliable?

Backblaze breaks down its data in two ways — by manufacturer, and by specific drive. The data is fairly complex, but we’ll try to break it down into morsels of easy-to-digest, actionable information. (Read: How a hard drive works.)
As of the end of December 2013, Backblaze had 12,765  Seagate drives, 12,956 Hitachi drives, and 2,838 Western Digital drives. These drives are not all the same age — some are almost four years old, while many were installed in the past year. The odd numbers are because Backblaze basically buys whatever drive offers the most competitive dollar-per-gigabyte ratio, with reliability being a secondary factor. For most of the last four years, Seagate and Hitachi have offered the best price-per-gig, with Western Digital Red drives only now becoming a viable option for Backblaze.

Hard drive annual failure rate, broken down by maker (Hitachi, Seagate, Western Digital) and size

As you can see from the graph above, Hitachi drives are by far the most reliable. Even though most of Backblaze’s Hitachi drives are now older than two years, they only have an annual failure rate of around 1%. The “annual failure rate” is the chance of a drive dying within a 12-month period. After three years of being powered up 24/7, 96.9% of Hitachi drives are still running.
Western Digital is slightly worse, but still impressive: After three years of operation, 94.8% of Western Digital drives are still running. Backblaze lists the annual failure rate of the WD drives at around 3% (I don’t think the numbers quite add up, but I could be wrong).
Seagate drives are not very reliable at all. As you can see in the second graph below, Seagate drives are fine for the first year, but failures quickly start building up after 18 months. By the end of the third year, just 73.5% of Backblaze’s Seagate drives are still running. This equates to an annual failure rate of 8-9%.

Hard drive failure rate, plotted by month

In Backblaze’s words: “If the price were right, we would be buying nothing but Hitachi drives. They have been rock solid, and have had a remarkably low failure rate.”

Which single hard drive is the most reliable? (And which is the least?)

In general, then, if you want a reliable hard drive you should go for a Hitachi or Western Digital. If you’re looking for a specific drive model that has good longevity, the numbers break down interestingly.
The two best drives, with 0.9% annual failure rate over more than two years, are the Hitachi GST Deskstar 5K3000, and Hitachi Deskstar 7K3000. Get one of these drives and you’re almost guaranteed (97-98%) to make it through three years without a dead drive. If you want a 4TB drive, the Hitachi Deskstar 5K4000 is your best bet — it has a slightly higher failure rate, but still below WD and Seagate’s offerings.
As far as poor reliability goes, Seagate has some nasty offenders. The 1.5TB Seagate Barracuda 7200 (an old drive now) has a very high chance of failing after three or four years. Even the newer 3TB Seagate Barracuda has a pretty high failure rate, at 9.8% per year.
Backblaze also notes that some drives (the Western Digital Green 3TB and Seagate Barracuda LP 2TB) start producing errors as soon as they’re slotted into a storage pod. They think this is due to the large amounts of vibration caused by thousands of other hard drives. (They also think that their aggressive spin-down setting, which is ostensibly to save power, causes a lot of wear to the drive.)
Hit up Backblaze’s website for a full list of hard drives and their statistics.

Samsung and Toshiba

Unfortunately, Backblaze doesn’t have a statistically significant number of Samsung or Toshiba drives installed. Even so, because Samsung’s hard drive division was acquired by Seagate in 2011, it’s hard to say if an older, pre-acquisition Samsung drive would be more or less reliable than a post-acquisition drive. Toshiba/Fujitsu still have a reasonable wedge (~10%) of the market share pie, but unfortunately we’ll have to wait for another study to see how they compare to Seagate, Western Digital, and Hitachi.
On the topic of acquisitions, you may also remember that Western Digital acquired Hitachi GST almost two years ago. If we compare Hitachi drives from before and after the acquisition, the annual failure rate seems to stay the same (around 1%). It would seem that Western Digital and Hitachi have the reliable hard drive business sewn up — and this is before we’ve had a chance to see what WD/HGST’s helium-filled hard drive can do!