In a hardware RAID solution, the controller passes whatever logical volume you tell it, and the OS sees that logical volume as a disk.
During the OS installation you may partition it as you see fit, just as you would a single disk.
Software-based RAID works much differently. Whereas hw raid is an array of disks...sw raid (regardless of which OS you're running) is an array of partitions on the disks.
Here's an example of software raid taken too far.