This counter indicates how many times the controller detected a bus fault for this drive, with 4,294,967,295 returned if the value cannot be determined. An admin treats a rising bus fault count as a sign of a connectivity or signal-integrity problem on the drive's bus rather than a media issue with the drive itself. For example, an increasing bus fault count paired with normal read/write error counts would point troubleshooting toward cabling or backplane connections instead of the disk.