When you deploy a VCSA, it creates 13 various sized disks. This is because VMware (the application) doesn't have a way of saying 'Create one LVM, and then split it into these chunks' - which is an annoyingly complex thing to do programatically.
You ALSO can't just make a single volume and mount everything as a single volume, because the VCSA wants to keep track of the '/storage/archive' volume, and clean things up there. But that's fine - we CAN do better, and we can make it a lot easier to manage, but you need to shut your VCSA down, and do some things in single user mode (not init=/bin/bash, as we need networking and LVM's up and working).
Note that you have to do this on the ESXi server that is HOSTING the vCenter server - you can't shut down vCenter and then expect to be able to manage it through vCenter!
Here's my VCSA before I do anything to it - and you'll notice that /storage/archive is already full.
What we need to do is add a new physical disk. I've created a single 200GB disk, and then attach it to the VM, and that appeared as /dev/sdn
(On hold - I can't update my VCSA, it won't stage the install and says "Error in method invocation Timeout happens while sending message to microservice" - will get back to this)