You never want to mix SSDs and HDDs in the same RAID array. The array should be all SSDs or all HDDs.
The Read/Write performance of a RAID-0 array is based upon the drive in the array with the slowest Read/Write speeds.
The total capacity of a RAID-0 array is based upon the drive in the array with the smallest size.
So if you RAID-0 a 30GB drive and a 500GB drive, your array's total capacity (before formatting) will be 60GB (30 x 2).
I have an Alienware M17xr4. It came with a factory raid boot drive using the ssd. For some reason I decided it would be a good idea to boot n nuke my system to start over. It wiped all partitions and the restore cd only installs windows on either of the drives. When I try making the raid volume, I created the 60Gb array, but it leaves the rest of my 500Gb drive useless. What I am asking is if there is a way to create a partition of my 500Gb hard drive that would be usable in a RAID array.