Basically, I borrowed these instructions from serverfault.com.
But once I got to the fsck step I started getting errors like `ext2fs_open2: Bad magic number in super-block`. Are these steps necessary for the thin pool? There's no filesystem for it to resize, is there? It shows the correct size in the GUI.LVM physical volume to extend the default pve-data LVM logical volume and /var/lib/vz filesystem:
- partition your device and set the LVM (8e) flag
- create a new physical volume with pvcreate /dev/<DEVNAME>
- extend default VG with vgextend pve /dev/<DEVNAME>
- extend data logical volume with lvextend /dev/mapper/pve-data /dev/<DEVNAME>
- verify your FS is clean with fsck -nv /dev/mapper/pve-data
- resize your FS with resize2fs -F /dev/mapper/pve-data