I have an SD card formatted as Mac OS Extended that was imaged with the Apple Diagnostics disk image. Holding option to boot to this SD card on a Mac works as expected.
I tried to use Disk Utility to convert the only volume on the SD card to APFS, and Disk Utility presents the error
An internal error has occurred. Operation failed…
Is there an alternate way to make this work or otherwise a way to figure out exactly what's going wrong with the APFS conversion? Thanks!
Just as an update, with a Mac OS Extended USB drive connected, this is the output of diskutil list.
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *251.0 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS Container disk1 250.8 GB disk0s2
/dev/disk1 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +250.8 GB disk1
Physical Store disk0s2
1: APFS Volume Macintosh HD 240.1 GB disk1s1
2: APFS Volume Preboot 19.7 MB disk1s2
3: APFS Volume Recovery 509.8 MB disk1s3
4: APFS Volume VM 1.1 GB disk1s4
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *15.8 GB disk3
1: EFI EFI 209.7 MB disk3s1
2: Apple_HFS AppleDiagnostics 15.5 GB disk3s
Best Answer
The only macOS version that can boot from a APFS container is High Sierra. In your case, the Apple_HFS volume does not contain not High Sierra. There is no way to convert to APFS and remain bootable.