To create ANY raid (using kernel's software RAID) you need to create two partitions and mark them as raid (it's the moment where you create a partition but instead formatting it you mark it as RAID) then of course go to RAID part of YaST partitioner and create a partition on that RAID-1. After that i propose You copy the relevant data to one of the disks that are part of that RAID-1 and the linux's kernel should take care of the rest.
It would be best to draw what you want to do
