Google Research suggests that more than 90 percent of new information produced is stored on magnetic media, mostly hard disk drives.
With so much data being stored this way just how long should we expect a hard drive to last?
First, let’s go over how hard drives work, and how they fail.
Hard Drive Primer
A hard drive operates in similar way to a record player. It has electric motors that power the spindle which spins the platters, and the actuator that positions the head to read and write the magnetically recorded data.
Modern hard drives have multiple stacked platters, each with its own read/write head to allow for greater data storage.
The platters typically rotate at speeds of 5,000 to 15,000 rpm with the head so close to the surface of the platter that the gap between them is measured in nanometers (i.e. very very very close).
How hard drives fail
There are typically three underlying causes of failure that strike during the life of a hard drive: (1) manufacturing defects that cause high failures during the first few months and fall to a lower ongoing rate, (2) failures due to components wearing out that start to grow after three or four years, and (3) catastrophic failures that occur at any time due to fire, flood, or shock.
Failures are grouped into two broad categories:
Physical Failure – the hard disk is one of the few mechanical components of your computer, and as with all things mechanical – it will eventually fail.
This can happen because one of the motors over heats, the drive bearings wear out, or a head fails. A head failure can occur when the read/write head crashes into the spinning platters (this is what where the term “hard drive crash” originates).
Logical Failure – This refers to corruption in a hard drive’s file structure or software, rather than the physical hardware.
Malware infections, human error, and corrupted firmware can all case logical failures. These failures can be so extensive that the system will not boot up or recognize the hard drive when it’s connected.
Ok, now let’s get back to question at hand.
Hard drives failure rates over time
Blackblaze looked at the performance of more than 25,000 drives over a 5 year period (to 2013) and found that drive failure rates vary by age but not as you’d probably think. They found failures followed the ‘bathtub curve’.
The idea of the bathtub curve is that defects come from three factors: (1) factory defects, resulting in “infant mortality”, (2) random failures, and (3) parts that wear out, resulting in failures after much use.
Backblaze produced the chart above commenting that the chart above shows the failure rate of drives in each quarter of their life. For the first 18 months, the failure rate is around 5%, then it drops, before going up substantially at about the 3-year point.
Breaking down this chart we see:
- For the first 1.5 years, drives fail at 5.1% per year
- For the next 1.5 years, drives fail less, at about 1.4% per year
- After 3 years though, failures rates skyrocket to 11.8% per year
Blackblaze also note that:
- 80% of drives last at least 4 years
- The estimated average life of a hard drive is 6 years.
Google (in 2007) also studied drive failure rates over time, reporting the follow results:
However the Google researchers note that:
“While it may be tempting to read this graph as strictly failure rate with drive age, drive model factors are strongly mixed into these data as well.
Consequently, these data are not directly useful in understanding the effects of disk age on failure rates (the exception being the first three data points, which are dominated by a relatively stable mix of disk drive models).
It is interesting to note that our 3-month, 6-months and 1-year data points do seem to indicate a noticeable influence of infant mortality phenomena, with 1-year AFR dropping significantly from the AFR observed in the first three months.”
These model specific results are also born out by Storelab who in a Russian study found some interesting results, and although the study is not large or scientific enough, it provides a useful insight into the hard drive market. While the hard drives from one manufacturer lasted 3.5 years on average, comparable models in capacity, features, and price from another manufacturer only lasted 1.5 years.
Wrap Up and Conclusion
Let’s be clear. Your hard drive is the most likely part of your system to fail, and probability of a hard drive failure is 100% (yes, that’s quite high). It is just a matter of time.
Both Google and Backblaze note that failure rates are “known to be highly correlated with drive models, manufacturers and vintages”. We will explore the most and least reliable brands in a later blog post.
So don’t play chicken with your hard drive. It might only last 10 days, maybe it will go 10 years. But it will go eventually.
If you have important data on a hard drive, you better make sure a copy of that data lives somewhere else as well.