106 IBM System Storage N series Hardware Guide8.3.1 Planning Stretch MetroCluster configurationsFor planning and sizing Stretch MetroCluster environments, keep in mind theseconsiderations: Use multipath HA (MPHA) cabling. Use FibreBridges in conjunction with SAS Shelves (EXN3000 & EXN3500). N62x0 and N7950T systems require FC/VI cards for Fabric MetroClusters. Provide enough ports/loops to satisfy performance (plan additional adapters ifappropriate).Stretch MetroCluster controllers connect directly to local shelves and remote shelves. Theminimum is four FC ports per controller for a single stack (or loop) configuration. But keepin mind that you mix the pools of the different two controllers in each stack. For moreinformation, see Figure 8-4.This has a minimal effect on the environment, because in case of disk failures (+replacement), you must assign this disk manually to the correct controller/pool. Therefore,use disk pools on different stacks.Figure 8-4 Stretch MetroCluster setup with only one stack per site Stretch MetroCluster has no imposed spindle limits, just the platform limit. Take care in planning N6210 MetroCluster configurations, because the N6210 has onlytwo FC initiator onboard ports and two PCI expansion slots. Because you use one slot forthe FC/VI adapter, you have only one remaining slot for an FC initiator card. Because youneed four FC ports, needed for Stretch MetroCluster, two configurations are possible:– Two onboard FC ports + dual port FC initiator adapter– Quad port FC initiator HBA (frees up onboard FC ports)Remember that all slots are in use and the N6210 cannot be upgraded with otheradapters.Requirement: A Stretch MetroCluster solution requires at least four disk shelves.
