Switch from VmWare ESXi to Opennebula

I’m not really new to OpenNebula but I got a serious problem with what I was asked to do :
I was using an esx with free esxi on it, but was stucked by the non-free Vcenter that was necessary to build my lab.
So I was asked to move to Opennebula.
I format my esxi OS (300Go raid 1) and installed ubuntu with the opennebula package.
But I can’t get my old datastore (vmfs from my previous vmware) working.
I can’t format those disks because I got fully functionnal Vms on them (3.3TB total space), and I’d like to import my vms on Opennebula.

Did I do something wrong? Or am I just missing something important? I can’t find answers to my questions, and I’m searching for 5 days now.

Could someone please give me a hand? Thanks a lot, and sorry for my english, I’m french…

Versions of the related components and OS (frontend, hypervisors, VMs):
OpenNebula 5.6.1 / Ubuntu 18.04 / Dell PowerEdge R530
Steps to reproduce:

Current results:

Expected results: