With a 6 node Lefthand cluster, I'd consider to create multiple LUNs for better load distribution. Each LUN will have a managing controller, and with only a single production LUN you will concentrate traffic on one node and therefore loose the benefits of the Lefthand design. In this Mutli-Site cluster you plan, you will usually have 4 Managers (two on each site) and one Failover Manager (FOM), so I'd suggest at least 4 LUNs.
André