108 IBM System Storage N series Hardware Guide8.3.1 Planning Stretch MetroCluster configurationsFor planning and sizing Stretch MetroCluster environments, remember the followingconsiderations: Use multipath HA (MPHA) cabling. Use FibreBridges with SAS Shelves (EXN3000 & EXN3500). N62x0 and N7950T systems require FC/VI cards for Fabric MetroClusters. Provide enough ports or loops to satisfy performance (plan for more 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. However,you mix the pools of the different two controllers in each stack, as shown in Figure 8-4.Figure 8-4 Stretch MetroCluster setup with only one stack per siteBecause of the SyncMirror feature and the mirrored plexes (pool0 and pool1), disk failureshave no operational impact. All disks, including spare disks, must be manually assigned toeach pool.MetroCluster design features the following important considerations: Stretch MetroCluster has no imposed spindle limits, only the platform limit. Take care in planning N6210 MetroCluster configurations because the N6210 has only twoFC initiator onboard ports and two PCI expansion slots. Because you use one slot for theFC/VI adapter, you have only one remaining slot for an FC initiator card. Because youneed four FC ports, which are needed for Stretch MetroCluster, the followingconfigurations are possible:– Two onboard FC ports + dual port FC initiator adapter– Quad port FC initiator HBA (frees up onboard FC ports)All slots are used and the N6210 cannot be upgraded with other adapters.Requirement: A Stretch MetroCluster solution requires at least four disk shelves.
