You should (also) be looking at it from the LVM perspective, to see exactly what is what.
vgs
vgdisplay
lvs
lvdisplay
and so on.
Proxmox uses LVM by default and allocates linux volumes to its virtual machines (kvm) and to its containers (lxc), but by default it also uses a thin pool - that's a feature in lvm that uses dynamically allocated space, so that you have a more efficient use of space. If you preallocated space, then you can't (easily) change it afterwards. But using thin pools can also be risky, of course, 'cause if you run out of a space it's usually more dangerous than running out of ram or cpu and the VM usually 'think' they have more space available than they actually have.
I think vgdisplay (or vgs) should tell if you if you're using a thin-pool, there should be a 't' flag somewhere.
They might call 'pve' the physical volume, I don't remember exactly. LVM consists of three layers:
physical disks,
volume groups,
linux volumes. A physical disk is usually linux partition. A volume group can span several physical disks (you can create arrays). And linux volumes reside inside volume groups. So inside the linux volumes you can format that space to create the actual filesystem, which in turn can eventually be used for storing the 'real' data.
Anyway, what you see there is a notation used by proxmox. It might be physical disk + linux volume or rather volume group + linux volume, don't remember exactly.
In any case, there are a lot of useful lvm tutorials on the internet, for instance:
https://www.digitalocean.com/communi...and-operations
