OK, disks to be used in Unraid need to be formatted by Unraid or the UD plugin, or they won't be accepted, you can also use the UD plugin to mount the disks for the copy or add them to the array, without parity it will function similarly, though in the array you can already use user shares to split the data over multiple disks, if needed, copy will need to be done manually, but you can use Midnight Commander (mc on the console) or the Krusader docker, both have a GUI.