Controller-to-shelf-connection rules

Each controller connects to the first and last disk shelf in each stack in the system through the controller SAS ports. The controller SAS A and C ports connect to the first disk shelf square ports. The controller SAS B and D ports connect to the last disk shelf circle ports. These controller SAS ports can be on a SAS HBA in a physical PCI slot (slot 1-N) or on the base controller.

The SAS cabling algorithm described in this document balances SAS cabling between the onboard SAS ports (as applicable) and SAS HBA ports to provide highly available storage-controller configurations. This cabling algorithm meets the following goals:

Provides a single, easily understood universal algorithm for all SAS products and configurations.
Is verifiable by configuration-checking software and tools.
Provides maximum possible resilience to maintain availability and minimize the reliance on controller takeovers.

Any deviations from the algorithm are not recommended; deviations may reduce reliability, universality, and commonality.

Note: If your system cabling is not compliant with the rules in this guide, it is recommended that you correct the cabling during a maintenance window.

A and C port connections

Controller SAS ports A and C are connected to the first disk-shelf square port in each stack of disk shelves.
The A and C ports on controller 1/A connect to IOM A. The A and C ports on controller 2/B connect to IOM B.

For example, the following illustration shows how controller ports A and C are connected to disk shelves that have the IOMs arranged side by side, similar to how a EXN3500 disk shelf is oriented:

For example, the following illustration shows how controller ports A and C are connected to disk shelves that have the IOMs arranged one above the other, similar to how a EXN3000 disk shelf is oriented:
Controller SAS ports A and C are connected to the disk-shelf stacks in sequential order of the PCI slots (slot 0, slot 1, slot 2, and so on) on the controller.
For example, a controller with slots 1, 2, and 3 occupied with quad-port SAS HBAs is cabled in order of slots and ports 1a, 2a, 3a, 1c, 2c, 3c:

For example, a controller with slots 0, 1, and 2 occupied (slot 0 being an onboard port and slot 1 and slot 2 being quad-port SAS HBAs) is cabled in order of slots and ports 0a, 1a, 2a, 1c, 2c:

B and D port connections

Controller SAS ports B and D are connected to the last disk-shelf circle port in each stack of disk shelves.
The B and D ports on controller 1/A connect to IOM B. The B and D ports on controller 2/B connect to IOM A.

For example, the following illustration shows how controller ports B and D are connected to disk shelves that have the IOMs arranged side by side, similar to how a EXN3500 disk shelf is oriented:

For example, the following illustration shows how controller ports B and D are connected to disk shelves that have the IOMs arranged one above the other, similar to how a EXN3000 disk shelf is oriented:
Controller SAS ports B and D are connected to the disk-shelf stacks by offsetting the order of the PCI slots by one so that the first port on the first slot is cabled last.
The cabling offset ensures system resiliency.

For example, a controller with three quad-port SAS HBAs in slots 1, 2, and 3 is cabled in order of slots and ports 2b, 3b, 1d, 2d, 3d, 1b:

For example, a controller with slots 0, 1, and 2 occupied (slot 0 being an onboard port and slot 1 and 2 being quad-port SAS HBAs) is cabled in order of slots and ports 1b, 2b, 1d, 2d, 0b:

A controller with one quad-port HBA is cabled in order of port 1d and then 1b:

Stack cabling sequence

Controllers are cabled to the stacks according to the sequence of the stacks, such as stack 1, stack 2, stack 3, and so on.

N3400 configurations

For single-controller N3400 configurations, the controller is in Slot B (the bottom slot); therefore, the controller is cabled as if it were controller 2/B. If a second controller is added to make this an HA pair configuration, the new controller is cabled as controller 1/A.