DiskGradeHow the grades work
Where the data comes from
Every figure on this site is computed from Backblaze Drive Stats. Backblaze is a cloud storage company that publishes a daily record of every drive in its data centres: which model it is, and whether it failed that day. We thank Backblaze for making this data public. DiskGrade is not affiliated with Backblaze.
This site currently covers Q1 2023 to Q3 2026: 1,124,223 drive-years and 17,073 failures across 99 models. We add each new quarter after Backblaze publishes it.
Failure rate
For each model we count drive-days (one drive running for one day) and failures. The annualised failure rate is failures divided by drive-years:
failure rate = failures ÷ (drive-days ÷ 365) × 100
A rate of 1% means that out of 100 drives running for a year, one is expected to fail. This is the same calculation Backblaze uses.
Grades
| Grade | Meaning | Failure rate / year |
|---|---|---|
| A | Excellent | up to 0.6% |
| B | Good | up to 1.2% |
| C | Average | up to 2% |
| D | Below average | up to 3.5% |
| F | Poor | over 3.5% |
A model is graded only when it has at least 100,000 drive-days on record. With less running time, one or two failures move the rate too far to trust, so we show the figure but no grade. Models with fewer than 10,000 drive-days are left out altogether.
What the grades cannot tell you
- Data-centre use is not home use. These drives run all day in cooled, vibration-managed racks. A drive in a desktop PC or a home NAS faces different heat, power cycling and handling.
- Only models Backblaze buys are covered. That means mostly large enterprise and NAS-class drives. Many consumer drives and most SSDs are missing.
- A model number is not a product line. Results for one model say little about a different capacity or revision sold under the same name.
- Age matters. Old drives fail more often. A model that has been in service for years can look worse than a newer one for that reason alone.
- The past does not guarantee the future. A grade describes drives already in service, not the one you are about to buy.
Use the data
The full table is free to download as drive-grades.csv. If you use it, please credit Backblaze as the source of the underlying data, as their terms ask, and link to DiskGrade for the grades.