Exn3000 And Exn3500 Disk Shelves Cabling; Controller-To-Shelf Connection Rules - IBM N series Hardware Manual

6.1 EXN3000 and EXN3500 disk shelves cabling

This section describes cabling the disk shelf SAS connections and the optional ACP
connections for a new storage system installation. Cabling the EXN3500 is similar to the
EXN3000. As a result, the information that is provided is applicable for both.
As of this writing, the maximum distance between controller nodes that are connected to
EXN3000 disk shelves is 5 meters. HA pairs with EXN3000 shelves are local, mirrored, or a
stretch MetroCluster, depending on the licenses that are installed for cluster failover.
The EXN3000 shelves are not supported for MetroClusters that span separate sites, nor are
they supported for fabric-attached MetroClusters.
The example that is used throughout is an HA pair with two 4-port SAS-HBA controllers in
each N series controller. The configuration includes two SAS stacks, each of which has three
SAS shelves.
Important: We recommend that you always use HA (dual path) cabling for all shelves that
are attached to N series heads.

6.1.1 Controller-to-shelf connection rules

Each controller connects to each stack of disk shelves in the system through the controller
SAS ports. These ports can be A, B, C, and D, and can be on a SAS HBA in a physical PCI
slot [slot 1-N] or on the base controller.
For quad-port SAS HBAs, the controller-to-shelf connection rules ensure resiliency for the
storage system that is based on the ASIC chip design. Ports A and B are on one ASIC chip,
and ports C and D are on a second ASIC chip. Because ports A and C connect to the top
shelf and ports B and D connect to the bottom shelf in each stack, the controllers maintain
connectivity to the disk shelves if an ASIC chip fails.
Figure 6-1 shows a quad-port SAS HBA with the two ASIC chips and their designated ports.
Figure 6-1 Quad-port SAS HBA with two ASIC chips
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IBM System Storage N series Hardware Guide