Hardware RAID is finicky. It usually demands drives of the same size and speed. Storage Spaces is agnostic. Have a 500GB SSD, a 2TB HDD, and a 4TB HDD? Throw them all in the pool. The software abstracts the physical differences, allowing you to utilize your hardware investment fully.
New-VirtualDisk -StoragePoolFriendlyName "MyPool" -FriendlyName "MySpace" -Size 500GB -ResiliencySettingName Mirror windows storage spaces