They're not just comparing the faulty drives numbers. Maybe you misunderstood the way they presented the data: in the first table, the "Number of Drives" column refers to the total number of drives they studied for each model, not just the ones that failed. So they give the sample size and the rate of failure for each model.
Or are you saying that the difference in worldwide sales for each drive model somehow renders Backblaze's failure rates invalid? The size of the population is irrelevant unless the size of the sample exceeds a few percent of the total population you are examining.
Or are you saying that the difference in worldwide sales for each drive model somehow renders Backblaze's failure rates invalid? The size of the population is irrelevant unless the size of the sample exceeds a few percent of the total population you are examining.