On my Macbook Air currently running Mac OS 10.13, I noticed that the size of individual disks don't add up to the total size, it's not even close.
Couple of months back I had installed 3 MacOS in different container, once I was done I erased them. Now I need to keep only one OS and extend it's size.
Why can't I see all disks here?
How do I extend the size of 'macOS-highSierra' to maxim possible?
After much research and trial, I figured that extending a container wasn't possible. I had to backup the macOS-highSierra installation, then format the entire hard drive and restore the backup. I used Carbon Copy Cloner to create backup and restore.