Backblaze statistics: which HDD is the best

A year has passed since I first published statistics on the number of failures in individual models of hard drives on my blog, and now is a good time to update it.

As of December 31, 2014, the Backblaze data center had 41213 disks, which are used for our tariff plans with no limit on the size of disk space. This is more than 27134 disks at the end of 2013. Last year, most of the new drives had a volume of 4 terabytes, and some 6 terabytes.

Failure statistics for 2014

Let's get right to the point. The table below shows the percentage of failures for 2014. Only models are shown, which we have more than 45 copies. I chose the number 45, because this is the number of disks in the Backblaze Storage Pod and this is usually enough to get meaningful percentages of failures, if they have worked for a sufficient time.
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Name / Model	Volume	amount drives	Average age in years	Annual failure rate	95% trust interval
HGST Deskstar 7K2000 (HDS722020ALA330)	2.0 TB	4,641	3.9	1.1%	0.8% - 1.4%
HGST Deskstar 5K3000 (HDS5C3030ALA630)	3.0 TB	4,595	2.6	0.6%	0.4% - 0.9%
HGST Deskstar 7K3000 (HDS723030ALA640)	3.0 TB	1,016	3.1	2.3%	1.4% - 3.4%
HGST Deskstar 5K4000 (HDS5C4040ALE630)	4.0 TB	2,598	1.8	0.9%	0.6% - 1.4%
HGST Megascale 4000 (HGST HMS5C4040ALE640)	4.0 TB	6,949	0.4	1.4%	1.0% - 2.0%
HGST Megascale 4000.B (HGST HMS5C4040BLE640)	4.0 TB	3,103	0.7	0.5%	0.2% - 1.0%
Seagate Barracuda 7200.11 (ST31500341AS)	1.5 TB	306	4.7	23.5%	18.9% - 28.9%
Seagate Barracuda LP (ST31500541AS)	1.5 TB	1,505	4.9	9.5%	8.1% - 11.1%
Seagate Barracuda 7200.14 (ST3000DM001)	3.0 TB	1,163	2.2	43.1%	40.8% - 45.4%
Seagate Barracuda XT (ST33000651AS)	3.0 TB	279	2.9	4.8%	2.6% - 8.0%
Seagate Barracuda XT (ST4000DX000)	4.0 TB	177	1.7	1.1%	0.1% - 4.1%
Seagate Desktop HDD.15 (ST4000DM000)	4.0 TB	12,098	0.9	2.6%	2.3% - 2.9%
Seagate 6 TB SATA 3.5 (ST6000DX000)	6.0 TB	45	0.4	0.0%	0.0% - 21.1%
Toshiba DT01ACA Series (TOSHIBA DT01ACA300)	3.0 TB	47	1.7	3.7%	0.4% - 13.3%
Western Digital Red 3 TB (WDC WD30EFRX)	3.0 TB	859	0.9	6.9%	5.0% - 9.3%
Western Digital 4 TB (WDC WD40EFRX)	4.0 TB	45	0.8	0.0%	0.0% - 10.0%
Western Digital Red 6 TB (WDC WD60EFRX)	6.0 TB	270	0.1	3.1%	0.1% - 17.1%

Notes:

1. The total number of disks in table 39696. As was said, models are excluded from the table if there are less than 45 copies available as of December 31, 2014. We also removed the Storage Pod boot disks. If we add both these categories, then we have 41213 working disks.
2. Some of these HGST discs are manufactured under the previous Hitachi brand. We were asked to indicate the HGST brand, and we respected the request.

What does crash mean for Backblaze

A disk is recognized as failed if we remove it from the Storage Pod for one or several reasons:

1. The disk does not turn on or is not recognized in the OS.
2. The disk is not synchronized or does not save synchronization in the RAID.
3. SMART statistics give inappropriate values.

Sometimes we transfer information from old disks to new ones, as we recently did when transferring from 1.5 TB disks to 4 TB disks. This process is called migration and such failed disks are not considered to be failed because they are still operational.

What are the best HDD

4 TB drives performed well

We liked all the 4 TB drives we bought last year. For a reasonable price, you get a large amount, and they have really few failures. The cheapest is Seagate Desktop HDD.15, and we have a lot of such disks. More than 12 thousand. The percentage of failures is pleasantly small: 2.6% per year. Low price and reliability are good for business.

HGST disks, although a bit more expensive, showed an even smaller percentage of failures: 1.4%. This is not a significant difference to strongly influence the decision to buy, but when the cost decreases, we will buy some quantity. We also have more than 12 thousand such disks.

What with the disks WD 4 TB?

We have only one Storage Pod with Western Digital 4 TB drives. Why? The reason is simple: the price. We buy discs in bulk through different companies, and each time we received answers to our requests, WD discs were $ 15-20 more expensive than others. This is too much margin, given that the Seagate and HGST drives work well.

3 TB drives are not very good

HGST Deskstar 5K3000 3 TB drives have proven to be highly reliable, but they are expensive compared to other models (including similar 4 TB drives from HGST). The percentage of failures of Western Digital Red 3 TB at 7.6% is slightly higher, but acceptable. But Seagate Barracuda 7200.14 3 TB is another story. We will tell about their breakdowns in the next blog post.

Seagate 4TB Confidence

You may ask why the current 4 TB Seagate drives are much better than the 3 TB Seagate models purchased a couple of years ago. We ourselves are surprised. When 3 TB disks just appeared, in the first year of operation the percentage of failures was 9.3%. 4 TB drives in the first year show only 2.6% of failures. I'm pretty sure that 4 TB drives will work well in the following years.

6 TB and beyond: it is not yet clear

We are now transitioning from 4 TB disks to 6 TB. So far we have 270 Western Digital Red 6 TB drives, a failure rate of 3.1%, but these are only three failed HDDs. Statistics show that in the 95% confidence interval, the real level of failures lies somewhere in the range from 0.1% to 17.1%. It is necessary that these disks work longer and collect more statistics before we get reliable figures.

We have only 45 Seagate 6 TB SATA 3.5 drives, although they will soon bring a new batch. They work only a few months, but none have yet failed. Here, too, more data should be collected before publishing reliable statistics.