I believe a resource pool, is just a group of resources, so adding a resource pool of 2 devices is exactly the same as adding those 2 devices manually, (I normally use them as VM groups to backup though).

You might be able to do striping (combining 2 devices into 1) using ZFS in Proxmox, or I think LVM can but you'd be using the command line.

Thanks for the responses; it seems I can't really do it. I looked into ZFS but if I use that it halves the available disk space to 2TB. I'm using the VM for a media server and thought it would be better to have 1 4TB space instead of 2 2TB disks. At the end of the day it isn't a big deal, I just thought I'd be able to present both disks as 1.

As per the documentation, pools are basically just resource groups to make permission management easier, so they aren't really supposed to handle anything like that. Maybe look into a RAID setup of some sort or mergerfs if you just need file level pooling.

I think the question is if you want to add the external USB hard drives to Proxmox so that not just the mentioned Ubuntu VM but other VMs and LXCs can benefit from them or if you want them to be added exclusively to the Ubuntu VM and Ubuntu VM only.

If it is the latter, you can leverage USB device passthrough and passthrough the two drives to the VM in whole. Then you can do whatever you want with them inside the VM. You can use ZFS or BTRFS or mdadm to create a stripe aka RAID 0 config.

Sounds like you're passing the physical HDDs to the VM instead of creating a new virtual HDD file in your proxmox pool.

If you don't mind me asking, what are you trying to do with your VM?

Bump