Buying Guide: The Most Reliable 3.5″ Hard Drive of 2015

What is the best hard drive to buy? Over the past few years online storage company Backblaze have published reliability statistics for the drives they use. This is interesting for us because they use regular consumer products. We’ve also added some numbers regarding costumer returns.

At the beginning of 2015 Blackblaze had 39,690 drives in use. By the 31st December 2015 this number had grown to 56,224, consisting of 18 different models by four different manufacturers: HGST, Seagate, Toshiba, and WDC.


Disclaimer: at the end of the articles are links to various hard drives, on Prices listed below are accurate on the date posted (23 February 2016) but may have changed since. Please verify the accuracy of your order before you purchase. If you do decide to purchase we may earn a small commission.


Backblaze Hard Drive Statistics

The Failure Rates and Confidence Intervals are cumulative from Q2 2013 through Q4 2015. The Drive Count is the number of drives reporting as operational on 31 December 2015.


Backblaze hard drive stats 2015


From the above you can see that Backblaze uses mostly Seagate (31,400) and HGST (22,905) drives, and a relatively small number of Toshiba and WDC. As Backblaze state, “nearly all of the 16,000+ drives purchased in 2015 have been Seagate drives.”


During 2015, five drive models were retired and removed from service.

Backblaze hard drives removed 2015


Backblaze Hard Drive Reliability By Size

At the end of 2015 all 1TB WDC drives were retired and replaced by larger models. “The 1TB Western Digital drives performed well with many of the drives exceeding 6 years in service and a handful reaching 7 years before we replaced them. The cumulative annual failure rate was 5.74% in our environment, a solid performance.”

As for the 2TB models, Seagate units were also removed from service. “While their cumulative failure rate was slightly high at 10.1%, they were removed from service because we only had 225 of those drives.” Over 4,500 HGST drives remain in use, “and their cumulative failure rate is a meager 1.55%.”

For 3TB drives Backblaze also retired all Seagate models. The cumulative failure rate is 7.85% for all 3TB models combined, but is skewed due to the results of one particular drive: the Seagate ST3000DM001, which had a failure rate of 28.34%.

By the end of 2015 over 75% of drives in Backblaze’s datacenter are 4TB units. Nearly 70% are Seagate, 30% HGST, and a minute number are WDC and Toshiba drives. The average failure rate is 4.14%.

During 2015 more 6TB were added, “bringing the total to nearly 2,400 drives (1,882 Seagate, 485 Western Digital.)” The failure rates were 2.70% and 8.40% respectively.


backblaze drive failures barchart 2015


A Comment on Backblaze’s Results

It should be noted that Backblaze uses their drives in an environment that is not typical for consumers. As you will see below, the results for consumer use differ. That said, Backblaze’s results are nice to have and a great resource for those users who do run their drives 24/7.

While a number of Seagate models appear to have high failure rates in the past, this does not keep Backblaze from investing in more Seagate drives. This can be explained by, “Seagate drives … generally signal their impending failure via their SMART stats … and can take appropriate action.” And, “Drive failures from the other manufacturers appear to be less predictable via SMART stats.” In other words, when Backblaze notice that a drive is failing, they can swap it out for another unit. A luxury that does not apply to consumers, who probably do not keep spare drives around just in case their regular drive fails.

As you can read above, a failure rate of 5.74% Backblaze deems to be “a solid performance”, and a failure rate of 10.1% is “slightly high”. As a consumer I would class these failure rates as horrific. But it once again shows that Backblaze’s use of these drives should not be directly compared to our personal use. On their site Backblaze also indicate they purchase Seagate models, even though they have higher failure rates, instead of HGST, which obviously perform better, for reasons of availability and price. In other words, it’s a trade off. The way Backblaze have things set up, they feel comfortable going with Seagate drives.

Another thing to note if that it appears that, as drive storage space increases the failure rate tends to decline. In other words, quality of drives appear to be getting better. Whether this is due to better manufacturing processes, due to the technology used in the higher density drives, or due to the amount/size of platters used I do not know.


The Other Numbers: Consumer Returns

The following is an overview of percentages of drives returned to the manufacturer or dealer by consumers. These numbers are obtained from a retailer in France. All numbers are for drives sold more than 200 times, except those marked with an asterisk (*) where sales are between 100 and 200 units.


First off, here’s the list showing the average per manufacturer:

  • Seagate 0.60% (previously: 0.68%)
  • HGST 0.81% (previously: 1.16%)
  • Western 0.90% (previously: 1.09%)
  • Toshiba 0.96% (previously: 1.34%)

What immediately jumps out is that, in normal consumer use, Seagate drives have the lowest return rates!


2TB drives

  • 1.69% Toshiba DT01ACA200
  • 1.50% WD Black WD2003FZEX
  • 1.41% WD SE WD2000F9YZ (*)
  • 1.06% WD Purple WD20PURX
  • 0.97% Seagate Pipeline HD ST2000VM003
  • 0.94% Seagate Desktop SSHD ST2000DX001
  • 0.68% WD Green WD20EZRX
  • 0.65% Seagate NAS ST2000VN000
  • 0.63% Seagate Barracuda 7200.14 ST2000DM001
  • 0.59% WD Red Pro WD2001FFSX (*)
  • 0.44% WD Red WD20EFRX (Backblaze: 9.92%)
  • 0.41% WD RE WD2000FYYZ
  • 0.24% Seagate surveillance ST2000VX000
  • 0.00% Seagate Enterprise Capacity ST2000NM0033 (*)
  • 0.00% Toshiba PA4292E-1HL0 (*)


3TB drives:

  • 4.90% Toshiba DT01ACA300 (*) (Backblaze: 3.83%)
  • 1.94% WD SE WD3000F9YZ (*)
  • 1.60% WD Green WD30EZRX
  • 1.31% Seagate Barracuda 7200.14 ST3000DM001
  • 1.25% Toshiba PA4293E-1HN0 (*)
  • 1.23% WD Red WD30EFRX (Backblaze: 7.27%)
  • 1.23% Seagate NAS ST3000VN000
  • 1.16% WD Red Pro WD3001FFSX
  • 0.94% Seagate Surveillance ST3000VX000
  • 0.71% WD Black WD3003FZEX (*)


4TB drives:

  • 2.86% WD Re WD4000FYYZ (*)
  • 2.23% WD Black WD4003FZEX (*)
  • 1.53% WD Green WD40EZRX
  • 1.40% WD Red WD40EFRX (Backblaze: 2.43%)
  • 1.32% Seagate Desktop SSHD ST4000DX001 (*)
  • 0.82% Seagate Constellation ES ST4000NM0033
  • 0.71% Seagate Desktop HDD.15 ST4000DM000 (Backblaze: 2.19%)
  • 0.47% Seagate NAS HDD ST4000VN000
  • 0.00% HGST Deskstar 7K4000 H3IK40003272SE
  • 0.00% HGST Deskstar NAS 0S03665


5TB and 6TB drives:

  • 1.47% WD Red WD60EFRX (Backblaze: 5.81%)
  • 0.41% WD Green WD60EZRX
  • 0.00% WD Red WD50EFRX


A Comment On Consumer Returns Results

The biggest question here is the accuracy of the numbers. All we know from the French e-tailer’s numbers are that most of the drives listed have sold more than 200 units each. But not exactly how many each. For example, if a unit sold 201 pieces and 1 was returned, this means a return rate of 0.5%.  I would feel a lot more comfortable if we knew, for example, the same drive sold 2000 times and 10 were returned. The return rate would be the same, but then we’d know it’d be an accurate result.


Conclusion and Recommendation

It’s obvious from the above that all manufacturers have had drives that have had higher failure rates.

Recommendation for 24/7 users:


Recommendation for regular users:






Note that there may be other reasons for choosing a particular drive apart from reliability and size. For example, power consumption and performance can also be a consideration. A 6TB drive can use 9W, while a 4TB drive uses 5.6W. Generally 7200rpm models are desktop drives, and perform better than the 5400, 5700 or 5900rpm models used for storage/back-up or in a NAS.

Summing up, 4TB drives are currently the best bang-for-the-buck. This would make the $158 HGST HMS5C4040BLE640 for desktop and 24/7 use, and the $142.99 Seagate NAS HDD ST4000VN000 for back-up, our picks of the bunch.


Disclaimer: prices listed are accurate on the date posted (23 February 2016) but may have changed afterwards. Please verify the accuracy of your order before you purchase. If you do decide to purchase we may earn a small commission.

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