Code:A volume group called 'pve' already exists.
This is very simple.
You have an existing installation on you system drives/raid arrays
The Proxmox installer is a live linux environment. It scans all availble local storage devices, and detects all available LVM groups.
Since you had previously installed proxmox onto a local disk, this LVM group, 'pve', already exists.
Minor oversight of the Proxmox installer.
Boot up something else and erase all partition tables.
Cheers