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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
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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.

  • Thanks! I tried that command, and I get the error Error starting conversion from HFS to APFS: The given file system is not supported on APFS (-69618). The volume is formatted as Mac OS Extended. – Jake3231 Feb 4 '18 at 16:50
  • I updated my question. – Jake3231 Feb 4 '18 at 16:54
  • Thank you. There is no way to convert this volume to APFS? I know the bootable macOS volume can be converted, so I would be surprised if there is no way to do this. – Jake3231 Feb 4 '18 at 16:59
  • Well, you have a good point. You may be able to convert to APFS when the operating system is going to be High Sierra. In your case, the SD card is not booting to High Sierra. – David Anderson Feb 4 '18 at 17:04
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The Disk Utility UI only shows the errors number [Error starting conversion from HFS to APFS: The given file system is not supported on APFS (-69618)].

Whereas the commandline tool diskutil shows a more descriptive error:

Conversion to APFS of a macOS system volume is only allowed in the OS Installer Environment

I suggest trying to convert in the Recovery Partition / Internet Recovery or building a bootable Installer-USB-stick for either macOS High Sierra or Mojave.

Here's the whole terminal output:

$ diskutil apfs convert disk0s3 -dryrun
Started APFS operation on disk0s3 Mojave
Dry run of HFS Volume conversion to an APFS Container with a single APFS Volume
The target is the Journaled HFS+ volume "Mojave" backed by the GPT partition disk0s3
The target is a macOS system disk
Exiting conversion operations with error code -69546
Error: -69546: Conversion to APFS of a macOS system volume is only allowed in the OS Installer Environment

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