LVM 2 USB disks persistently

I am building myself a portable media player using the shell of a old NES. Inside i got a Rpi2 + a PiHut power usb hub + 2x1.5Tb WD portable disk (taped to the underside of the lid.

Now what i would like to accomplish is have LVM combine the two disk into 1. And then make OSMC see that disk and use it to stream movies/series from. I got LVM2 installed and have succeeded to create a single disk with. But… once i reboot OSMC does not see the two disks anymore.

I would very much like to make the lvm group work after reboot but i am stuck at what to do next.
The thing is… when i go into Kodi/OSMC and choose Exit plus Esc to get the commandline i can install the kvm group. When i then go back to kodi i do see the lvm group listed as storage. Until i reboot :frowning:

Thanks for reading this and also thanks for any advice given.

The PiNeS can been seen here: