Move VM to new version

Currently running 1.9 and only have 1 machine I really need to save before upgrading to 3. Trying to export it to an external USB drive, but I cant seem to mount the drive. Proxmox sees it when I connect it, and shows it as sdg1, but when I try to define it with <pvcreate /dev/sdg1> it tells me device not found.
Trying to follow instructions from this page - http://pve.proxmox.com/wiki/Storage_..._Local_Backing