A step-by-step account of how Disk Arbitration and APFS mount an external disk, from handling its partitions, to performing trims.
mount
Update adds a 22nd tool, to display a log extract tailored to examining the mounting of APFS disks. Also valuable for any APFS investigation.
Traced from recognition of the cable connection, through establishing PCI streams, to mounting the volume with APFS, and the bonus of a good trim at the end.
You have double-clicked on a disk image, and macOS refuses. Here is what you can do to get that image to mount, even when it’s damaged.
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