I had some free time so I decided to punch the numbers into a spreadsheet for further investigation.
If you look right below the data provided by backblaze, you can see I tabulated a drive failures per 1,000,00 drive days. As you can see, Seagate is by far the highest here. The problem with this figure and Annual failure rate is it doesn't really tell you how old each drive is on average. This is important as drive failure rate, at least in backblaze's case, increases after 3 years and spikes after 5. I have provided a chart from backblaze below demonstrating this. With this in mind, I thought it would be prudent to figure out on average where each drive would land on that failure curve. Please look at the bottom of my provided graphic and I will continue discussion just below it.
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As you can see above, on average backblaze's seagate drives have been in service for longer than your typical 5 year enterprise drive warranty. If you look at the chart provided by backblaze below, it's actually surprising that failure rate isn't higher given the number of service hours these drives have seen. HGST looks the best here as it has an even higher number of drives that have on average been in service longer than the warranty. The WDC drive numbers bear out what I said before, there simply isn't enough of a sample size here and of those we do have most haven't even seen 2 years of service yet. The only thing we could perhaps gleam from the WDC numbers is that at least with those SKUs they do not appear to be shipping out a lot of DOAs from the factory, assuming of course that backblaze even counts those drives towards these numbers (if you know whether they do or not LMK).
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Ultimately though there is a problem with both backblaze's numbers and my numbers. It's the fact that we don't know the age of each individual drive or the age of each bulk group of drives that backblaze purchases in groups that would all have the same age. This is a problem because it means that large groups of drives could be failing in a single quarter simply because they both have a high service life and are all the same age. This alone can result in spikes in AFRs. It's particularly problematic as this phenomenon is not always observable. It's possible 10,000 drives of a specific SKU are EOL and set to fail within 0 - 2 years yet the total drive service days can be small as backblaze could have possibly purchased 20,000 or more at a later date which makes the total service hours look much lower than a bunch of failing drives would otherwise suggest. If you assume the former drives are past 5 years service and the newer drives only have 1-2 years that could make it seem like the drives have a higher AFR simply because a large amount of older drives are reaching EOL that isn't reflected in the data provided publically.
Of course the data is useful but you have to take these factors into consideration. Given the above and the potential for spikes, I'd say that a 1-2% difference isn't that significant. Backblaze likely has far more rich data than they externally provide that they base their purchasing decisions on.