Server 2008 raid 5 set up

hi all i am trying to set up a file server on server2008 using raid5 with 8 1Tb drives it shows i have 6Tb when server 2008 is installed it shows two partitions the first is 2Tb the other is 4Tb but i can not do anything with the 4Tb do i need to use partitioning software.
can anyone help??