Backblaze calculated three distinct failure rates:
● 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.
The chart below shows that nearly 80% of all drives Backblaze has purchased are still operational.
Blackblaze has been running for five years and so doesn't have data for drives older than that; however, they extrapolated the line from the previous chart to estimate the point at which half of the drives have died, determining that, "The median lifespan of a drive will be over 6 years."
Many more details in the full report linked below...