If SMART logs show no errors but OS shows I/O errors, what could be the problem?

• A. The drive is healthy.
• B. Could be controller, cable, file system, or RAID problem.
• C. The OS must be corrupted.
• D. All SMART indicators are normal.

Answer: (B)

When SMART reports no errors, it means the disk’s internal health looks good. If the OS still shows I/O errors, the issue is more likely in the data path or storage subsystem rather than the drive itself. Possible culprits include the controller (SATA/SAS or RAID controller), the cables or connectors, the RAID configuration or health, or the file system itself being corrupted. A healthy drive with a failing cable, a misbehaving controller, a problematic RAID setup, or a corrupted filesystem can all produce I/O errors seen by the OS. To diagnose, inspect and swap cables, test the drive on a different controller/port, check RAID health and configuration, and run a file system check.