Backblaze disk drive failure stats suggest the “bathtub curve” effect may be imaginary.
The idea is that disk drives fail either early on in their life or after many years, and a plot of failure rate over time shows a U-shaped curve with higher rates at the start and end of working life and few or no failures between these points. However, a Backblaze blog shows that the bathtub curve effect is absent as the company builds up more lifetime failure data.
The bathtub curve concept looks like this:
Backblaze published three sets of HDD lifetime failure rate charts in 2013, 2021, and 2025. It has combined these in a single bar chart with trend lines added for each year:
There was a partial bathtub effect in 2013 (blue bars and curve), with a midlife failure rate peak as well as start and end-of-life peaks. The 2021 numbers (yellow bars and curve) differ, showing a mild early years rise and a pronounced end-of-life increase in failure rates.
The 2025 numbers (red bars and curve) are different again, showing a gradually rising failure rate curve until year seven, after which there is a drop and then a much less-pronounced uplift.
What is going on?
First of all, the number of drives involved has risen over the years, so the failure rates are more statistically reliable. In 2013, there were 35,000 drives, 207,000 in 2021, and as of June 30, 2025, Backblaze had 321,201 drives under management. Secondly, Backblaze could be managing its drives better. Thirdly, as these stats cover 15 years or more, the disk drive manufacturers are making more reliable drives.
The Backblaze bloggers say that “drives are getting better and lasting longer.” In effect, the bathtub disk drive failure rate concept looks to be wrong.
They add: “Our numbers have always and will always reflect both good planning and the unforeseen aspects of reality. Understanding whether drives are ‘good’ or ‘bad’ is always a conversation between what you theorize (in this case, the bathtub curve) and what happens (the Drive Stats dataset).”
You can access their drive stats database here.
