Friday, February 2nd 2018

Backblaze Releases Hard Drive Stats for 2017, HGST Most Reliable

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At the end of 2017 we had 93,240 spinning hard drives. Of that number, there were 1,935 boot drives and 91,305 data drives. This post looks at the hard drive statistics of the data drives we monitor. We'll review the stats for Q4 2017, all of 2017, and the lifetime statistics for all of the drives Backblaze has used in our cloud storage data centers since we started keeping track.

Hard Drive Reliability Statistics for Q4 2017
At the end of Q4 2017 Backblaze was monitoring 91,305 hard drives used to store data. For our evaluation we remove from consideration those drives which were used for testing purposes and those drive models for which we did not have at least 45 drives (read why after the chart). This leaves us with 91,243 hard drives. The table below is for the period of Q4 2017.
A few things to remember when viewing this chart:Bulking Up and Adding On Storage
Looking back over 2017, we not only added new drives, we "bulked up" by swapping out functional and smaller 2, 3, and 4TB drives with larger 8, 10, and 12TB drives. The changes in drive quantity by quarter are shown in the chart below:
For 2017 we added 25,746 new drives, and lost 6,442 drives to retirement for a net of 19,304 drives. When you look at storage space, we added 230 petabytes and retired 19 petabytes, netting us an additional 211 petabytes of storage in our data center in 2017.

2017 Hard Drive Failure Stats
Below are the lifetime hard drive failure statistics for the hard drive models that were operational at the end of Q4 2017. As with the quarterly results above, we have removed any non-production drives and any models that had fewer than 45 drives.
The chart above gives us the lifetime view of the various drive models in our data center. The Q4 2017 chart at the beginning of the post gives us a snapshot of the most recent quarter of the same models.

Let's take a look at the same models over time, in our case over the past 3 years (2015 through 2017), by looking at the annual failure rates for each of those years.
The failure rate for each year is calculated for just that year. In looking at the results the following observations can be made:

The failure rates for both of the 6 TB models, Seagate and WDC, have decreased over the years while the number of drives has stayed fairly consistent from year to year.
While it looks like the failure rates for the 3 TB WDC drives have also decreased, you'll notice that we migrated out nearly 1,000 of these WDC drives in 2017. While the remaining 180 WDC 3 TB drives are performing very well, decreasing the data set that dramatically makes trend analysis suspect.
The Toshiba 5 TB model and the HGST 8 TB model had zero failures over the last year. That's impressive, but with only 45 drives in use for each model, not statistically useful.
The HGST/Hitachi 4 TB models delivered sub 1.0% failure rates for each of the three years. Amazing.

A Few More Numbers
To save you countless hours of looking, we've culled through the data to uncover the following tidbits regarding our ever changing hard drive farm.
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