When installing Arch Linux, the guide usually starts with creating some install medium (a USB drive). However, there isn’t a lot of explanation about what that installation medium does.
If you already have an Arch machine, and you’re trying to install a new hard drive on the machine that already has an Arch installation. Skip the step of creating an installation medium. This is going to save you a lot of time and hassle in setting up your install envioronment. In using an external install medium, it just adds more work to be able to get to the point where you’re installing the OS. Some of that work involves connecting to the network in a new environment, setting up the system clock, etc. This is more work than what’s really needed.
Ok, so you already have an Arch system. If you have the newer drive plugged in, make sure you have Arch booted, and the new drive can be seen. Also keep taps where your new drives are showing up.
Install the Aur package arch-install-scripts. This will give you the arch-chroot package that you’ll need to chroot into the new environment.
Once you have the package, then you can move to the Partition the disks part of the guide and proceed as if you had done the previous steps.
This will also help you when booting the new drive. You should be able to select the new drive in the BIOS to boot rather than having to deal with booting from the USB or the new drive.