I'm happy to say that i was finally able to solve the issue, this involves destroying the datas inside the previous RAID.
I have open the ServerRAID GUI before entering OMV, removed every previous configuration and done this:
1x RAID 1 with 2x 500GB SAD drive
1x RAID 1 with 2x 1.2TB SAS drive
As said by geaves i'm now able to see the single drive in OMV for each RAID configured in the controller.
Hoperfully i have multiple copies of the data around some other machines (and NAS) to take back my files, and I can now copy them in the "new" drive in OMV.
Thank you for your input