Convert MTBF to AFR, and Read Both Correctly

MTBF converted to a yearly failure rate

How the conversion works

A drive that runs all year runs for 8,760 hours. Dividing that by the MTBF gives the expected failures per drive per year: 8,760 divided by 1,000,000 is 0.00876, or 0.876%. The exponential form, one minus e to the power of minus that number, gives the share of drives that fail at least once, 0.872%. At these sizes the two differ only in the third decimal place.

Both assume the drive is powered on all year. Seagate's SkyHawk manual states its figure for 8,760 power-on hours a year, over a three-year service life, in stated temperature and workload conditions.

The pairs on Seagate's data sheets, by product line

What the number is not

It is not a lifespan. An MTBF of 1,000,000 hours is 114 years, and the same sheets carry warranties of three and five years. Seagate's manual says it directly, calling the AFR and MTBF a population statistic not relevant to individual units.

It is also a rating, set by the maker for stated conditions, not a measurement of drives in service.

A measured rate, for comparison

Backblaze publishes failure counts for the drives in its own data centres. Its Drive Stats snapshot for the second quarter of 2026 covers 354,415 drives, 1,498 failures and 31,553,350 drive days, and gives an annualized failure rate of 1.73%. Those figures work out as failures divided by drive days, times 365.

That is Backblaze's result for its fleet, its models and its conditions. It is higher than the rated figures in the table above, and it is a different kind of number: an observed rate across many models and ages, against a rating for one model.

Where the figures come from