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 provides information about cabling the disk shelf SAS connections and the
optional ACP connections for a new storage system installation. Cabling the EXN3500 is
much alike the EXN3000. As a result, the information provided is applicable for both.
At this time, the maximum distance between controller nodes that are connected to EXN3000
disk shelves is 5 meters. HA pairs with EXN3000 shelves are therefore either local, mirrored,
or a stretch MetroCluster depending on the licenses 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 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.

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 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
Connecting the Quad-port SAS HBAs follows these rules for connecting to SAS shelves:
HBA port A and port C always connect to the top storage expansion unit in a stack of
storage expansion units.
HBA port B and port D always connect to the bottom storage expansion unit in a stack of
storage expansion units.
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IBM System Storage N series Hardware Guide