IBM N Series Hardware Manual page 146

The normal platform spindle limits apply to the entire MetroCluster configuration. However,
because each controller sees all storage, the platform spindle limit applies to the entire
configuration. For example, if the spindle limit for N series N62x0 is n, then despite the two
controllers, the spindle limit for a N62x0 fabric MetroCluster configuration remains n.
Figure 9-4 shows an example of an N series Stretch MetroCluster environment. Fibre
Channel ports of the N series nodes are connected to the Fibre Channel ports on the
FibreBridge (FC1 and FC2). SAS ports of the first and last shelf in a stack are connected to
the SAS ports (SAS port A) on the FibreBridge. Each stack has two bridges. MetroCluster
uses at least four FibreBridges.
Figure 9-4 Stretch MetroCluster with FibreBridges
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IBM System Storage N series Hardware Guide