This issue has come up a few times on Discord. The question can be summarised like this:
My existing IOTstack installation is running out of space on my primary drive. I have another drive. How do I move the "volumes" directory to the new drive?
This example is based on a Raspberry Pi 4 which is booting from a 500GB USB3 SSD. I will show you how to use a 32GB USB3 "thumb drive" as the secondary drive and move ~/IOTstack/volumes
onto it.