Encrypt external drive in MacOS High Sierra


Connect the drive via USB. List mounted devices:

diskutil list

Format a disk of choice as HSF+ (Journaled)

diskutil eraseDisk JHFS+ <your custom name> GPT <drive id>

Encrypt the partition

diskutil cs convert <partition id> -passphrase

<partition id> looks like disk2s2 for the disk2 device. Choose it accordingly in your context.