An enterprise server? You mean two 250GB drives set up as RAID 1, don't you?
If you are putting all the storage for 4 VMs on a single disk (or better, disk pair), then partitioning the drive will just cause you to spend all of your time doing disk seeks. Put the storage for the VMs in four qcow2 files in one partition so its closer together. You can set cache=none so you don't duplicate disk cache on the host and guest.