I found this article Proxmox Boot Tool, here is the output of findmnt / :
root@dw-srv-p4:/# findmnt /
TARGET SOURCE FSTYPE OPTIONS
/ rpool/ROOT/pve-1 zfs rw,relatime,xattr,noacl
root@dw-srv-p4:/# cd /rpool/ROOT/pve-1
root@dw-srv-p4:/rpool/ROOT/pve-1# ls -al
total 1
drwxr-xr-x 2...