If you create a RAID10 with 4 disks of each 1TB, you end up with a 2TB virtual volume. That's what windows sees, that's what windows partitions. So you don't create a partition on the disks but on the virtual RAID volume instead; to which disk it actually gets written is 'irrelevant' to the operating system.
Your OS normally doesn't see the physical disks of a "Fake"RAID array using Windows-only drivers; because it hides them to avoid any confusion. You'll only see one big 2TB volume you can partition like it was a single 2TB disk.