Planning Stretch Metrocluster Configurations - IBM N Series Hardware Manual

8.3.1 Planning Stretch MetroCluster configurations

For planning and sizing Stretch MetroCluster environments, keep in mind these
considerations:
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 if
appropriate).
Requirement: A Stretch MetroCluster solution requires at least four disk shelves.
Stretch MetroCluster controllers connect directly to local shelves and remote shelves. The
minimum is four FC ports per controller for a single stack (or loop) configuration. But keep
in mind that you mix the pools of the different two controllers in each stack. For more
information, 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 only
two FC initiator onboard ports and two PCI expansion slots. Because you use one slot for
the FC/VI adapter, you have only one remaining slot for an FC initiator card. Because you
need 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 other
adapters.
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IBM System Storage N series Hardware Guide