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kIOReturnBadMedia
Why this is more serious than a format issue
kIOReturnBadMedia reports a media error. The storage path has a medium to address, but an operation encountered a condition the relevant driver treats as a media failure. Depending on the device family, that can reflect unreadable sectors, damaged or incompatible media, a failed translation layer, or a lower-level transport condition that the driver surfaces as a media error.
The status alone does not diagnose the physical cause. It is nevertheless a reason to preserve evidence and reduce writes, not to repeatedly rewrite or reformat the target. A successful retry does not erase the need to investigate if the data or medium is important, because intermittent errors can precede more complete failure.
Safer response
- Record the operation, offset or logical range, device identity, and system log messages near the failure.
- Prioritize read-only backup or imaging of accessible data before repair actions when the medium carries valuable information.
- Compare behavior through another reader, cable, port, or host only when that does not risk additional writes.
- Distinguish media failure from a missing device, power loss, or a generic I/O error in the incident record.
References
- Apple IOReturn.h reference
- Apple Disk Arbitration Programming Guide
- Apple IOKit Fundamentals: Architectural Overview
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