Most Reliable HDDs – Backblaze

This article, HDD Reliability Update – September 2014, was published by Brian Beach, principal engineer, on the blog of Backblaze, Inc.

At Backblaze we now have 34,881 drives and store over 100PB of data. We continually track how our disk drives are doing, which ones are reliable, and which ones need to be replaced.

I did a blog post back in January, called What HDD Should I Buy? It covered the reliability of each of the drive models that we use. This month I’m updating those numbers and sharing some surprising new findings.

Reliability of HDD Brands
Losing a disk drive at Backblaze is not a big deal. Every file we backup is replicated across multiple drives in the data center. When a drive fails, it is promptly replaced, and its data is restored. Even so, we still try to avoid failing drives, because replacing them costs money.

We carefully track which drives are doing well and which are not, to help us when selecting new drives to buy.

The good news is that the chart today looks a lot like the one from January, and that most of the drives are continuing to perform well. It’s nice when things are stable.

The surprising (and bad) news is that Seagate 3TB drives are failing a lot more, with their failure rate jumping from 9% to 15%. The Western Digital 3TB drives have also failed more, with their rate going up from 4% to 7%.

In the chart below, the grey bars are the failure rates up through the end of 2013, and the colored bars are the failure rates including all of the data up through the end of June, 2014.

HDD Annual Failure Rate
Colored bars are as of September 2014. Grey bars from previous analysis in January 2014.

You can see that all the Hitachi drives, the Seagate 1.5TB and 4TB, and Western Digital 1TB drives are all continuing to perform as well as they were before. But the Seagate and Western Digital 3TB drives failure rates are up quite a bit.

What is the likely cause of this?
It may be that those drives are less well-suited to the data center environment. Or it could be that getting them by drive farming and removing them from external USB enclosures caused problems. We’ll continue to monitor and report on how these drives perform in the future.

Should we switch to enterprise drives?
Assuming we continue to see a failure rate of 15% on these drives, would it make sense to switch to enterprise drives instead?

There are two answers to this question:

• Today on Amazon, a Seagate 3TB enterprise drive costs $235 versus a Seagate 3TB desktop drive costs $102. Most of the drives we get have a three-year warranty, making failures a non-issue from a cost perspective for that period. However, even if there were no warranty, a 15% annual failure rate on the consumer desktop drive and a 0% failure rate on the enterprise drive, the breakeven would be 10 years, which is longer than we expect to even run the drives for.
• The assumption that enterprise drives would work better than consumer drives has not been true in our tests. I analyzed both of these types of drives in our system and found that their failure rates in our environment were very similar – with the consumer drives actually being slightly more reliable.

Detailed Reliability of HDD Models
The table below shows the detailed breakdown of how many of which drives we have, how old they are on average, and what the failure rate is. It includes all drive models that we have at least 200 of. A couple of models are new to Backblaze and show a failure rate of ‘n/a’ because there isn’t enough data yet for reliable numbers.

Number of HDDs by Model at Backblaze

We use two different models of Seagate 3TB drives. The Barracuda 7200.14 is having problems, but the Barracuda XT is doing well with less than half the failure rate.

There is a similar pattern with the Seagate 1.5TB drives. The Barracuda 7200.11 is having problems, but the Barracuda LP is doing well.

Summary
While the failure rate of Seagate and Western Digital 3TB HDDs has started to rise, most of the consumer-grade drives in the Backblaze data center are continuing to perform well, and are a cost-effective way to provide unlimited online backup at a good price.