Disk structure diagrammed for comparison, from the partition table, to HFS+ and APFS volumes, with further references.
What you need to know about the APFS file system, its containers and volumes, so you can understand errors and how to repair them.
What you need to know about the HFS+ file system, so you can understand error reports and how to repair it using Disk Utility and other tools.
What you need to know about disk formatting using the GUID Partition Table (GPT) to understand its problems and how to repair it.
Apple says that if you run First Aid on a disk, each of its volumes is checked too. Is that really true?
What do you know about the hidden and unmounted EFI partition on all the disks you use with your Mac? It could be very important.
The fine line between precision and obscurity examined in the Finder, against Apple’s Style Guide, and its accuracy. And what does HD stand for?
The Finder, Disk Utility and Terminal show disks and volumes differently, according to their function. This can appear confusing in Catalina until it has been explained.
How does the volume structure differ between Fusion Drives in HFS+ and APFS formats? Does Disk Utility show an accurate picture?
With narrowing of the cost difference between Fusion Drives and full-size SSDs, it’s worth considering likely differences in working life.