It's usually a good idea to use disks or partitions with the same disk size - if any one is bigger then the other, then you end up having some amount of unused space, as the lower size will be used on both RAID entities.
Simulating RAID in VMware or VirtualBox just adds complexity to your tests.
You can also use RAID for partitions on a single hard disk. If you want to simulate hard disk failure, then make a lot of partitions to simulate replacement disks as well.
Actually it's not clear what you want to achieve and where you get stuck.
Last edited by Tinkster; 10-30-2010 at 05:17 PM.