Salut

You CANNOT just plug-in your hard drive(s) to the RAID card. You have to follow the user manual instructions of the RAID card to install the NEW drives, set the RAID1 array and THEN copy the files from the old drive(s) to the new RAID drives.
You have to keep the old drives in the NL box as before, set the RAID card with new HDs. If you want to use the old drives with the new RAID card, you'll have to backup all your data that is on the drives before setting the RAID arrays as this will DELETE all data from the old drives.