Want one external drive from which you can boot two (or more) different versions of macOS? Here’s how to make it.
partition
How does the volume structure differ between Fusion Drives in HFS+ and APFS formats? Does Disk Utility show an accurate picture?
I’ve got two volumes showing in the Finder. So how come diskutil list tells me I’ve got four disks with a total of 12 partitions?
In recent years, most Mac users have stopped partitioning drives into volumes. In High Sierra, you will probably want to use volumes again. Lots.
Disk Utility has a bug which can waste a lot of time trying to re-partition drives, and HFS+ creaks horribly.
Being a hybrid, naming disks and volumes can get complex in OS X. This article demystifies them.
How to repartition and install El Capitan afresh on an old iMac.
Could I partition a Western Digital 3 TB My Cloud drive?
The Eclectic Light Company 