To add to the other suggestions, I would delete all raid configs and then use the USC to make the raid 1 with the 300GB drives and install your OS on there. Once done, use OMSA to create the large 2nd virtual disk, convert it to GPT and partition and format it (in disk management). If you wish to use UEFI, you'll need to change this in the bios before installing the OS as the OS will make the (300GB) bootdisk GPT automatically (but it's then unbootable in bios mode).
This new server we just got have two non-visible 300GB HD and eight 400GB HD. I tried to install w2k8 r2 OS using USC (F10 key) but I did it wrong.  For some reason, the OS ended up on the 2000GB partition of the 2800GB Virtual Disk 0 (All eight 400GB in a raid-5).  I didn't specify the size of the partition during the setup so I'm assuimng the partition was created 2000GB because it' s in BIOS mode. I installed Server Administrator and I saw that the two 300GB HD have not been allocated.  So I put them in a raid-1. I will be reconfiguring the virtual disks again and reinstalling the OS.  What I want is the OS to be on the raid-1 300GB (C:) and a D: for raid-5 (2800GB). The question is...how do I go about doing that??????  This UEFI/GPT business seems to be more complex.
PE R510: Making disks both BIOS and GPT/UEFI?