Thanks Udo, My Raid firmware allows this and I was able to grow the raid volume.
On my installation I have sda1 (boot partition) and sda2 LVM /dev/mapper/pve-root and /dev/mapper/pve-data
The extra space is visible on sda:
Disk /dev/sda: 238.3 GB, 238370684928 bytes255 heads, 63...