The only limit to the virtual disk size on Dell's MD3k series is the maximum number of physical drives in a single disk group. For raid 5 this is 30, for raid 10 it is 44 and for raid 0 it is 45. When setting up a cluster, I usually use a 2GB Quorum. If it is a hyper-v setup I then use 2 or more virtual disks to spread the IO load. If it isn't for hyper-v, then the virtual disk layout depends on the application and storage needs.
How big can I grow a Virtual disk?  As above I have two Dell PE servers in a failover cluster with Windows 2008R2 Ent. The MD300 contains two Virtual Disks 1 x 50Gb disk as a the cluster quorum and 1 x 4TB which holds virtual machines. I would like to add 2 TB to the bigger Virtual Disk; would this be suitable?
MD3000 Max virtual disk Size