Backblaze Named the Most Reliable Hard Drives—and Those That Fail Most Frequently
Cloud storage provider Backblaze has released its latest hard drive reliability report, detailing statistics from the third quarter of 2025. The analysis identifies four HDD models that achieved a perfect zero-failure record and three models that exhibited unusually high failure rates.
Understanding the Numbers
Before diving into the specifics, Backblaze clarified what constitutes a drive failure. The company uses Smartmontools and Drive Sentinel to monitor SMART data every few minutes. A drive is flagged as failed if it reports read errors and cannot recover the data. On servers with SATA drives, a failed unit is immediately taken offline, whereas on SAS servers, drives are isolated at the architectural level without requiring a shutdown.
As of June 30, 2025, Backblaze managed 332,915 drives, with 328,348 used for data storage. The company is continuing to phase out smaller 4TB drives while expanding its fleet of high-capacity drives (20TB and larger), which now constitute 21% of the total at 67,939 units.
The overall Annualized Failure Rate (AFR) for the quarter rose to 1.55%, up from 1.36% in Q2. For comparison, the lifetime AFR for all drives under observation is 1.31%.
Top and Bottom Performers
The Most Reliable Drives (Zero Failures)
- Seagate HMS5C4040BLE640 (4TB)
- Seagate ST8000NM000A (8TB)
- Toshiba MG09ACA16TE (16TB)
- Toshiba MG11ACA24TE (24TB)
Notably, the 8TB Seagate model has a remarkable track record, with its last failure—a single instance—recorded back in Q3 2024.
Drives With the Highest Failure Rates
- Seagate ST10000NM0086 (10TB): 7.97% AFR
- Seagate ST14000NM0138 (14TB): 6.86% AFR
- Toshiba MG08ACA16TEY (16TB): 16.95% AFR
Backblaze noted that the astronomical failure rate for the 16TB Toshiba model was an anomaly. The issue stemmed from a firmware update process that incorrectly flagged the drives as failed. The company expects this model's statistics to normalize in the next report.