Lenovo DM120S Installation And Cabling Manual page 43

The following illustration highlights how controller ports B and D connect in a multipath HA configuration with
one quad-port HBA and two stacks of disk shelves. Connections to stack 1 are shown in blue. Connections
to stack 2 are shown in orange.
Port pair connection rules (for non DM3000x, DM5000x, or DM7000x configurations)
Controller SAS ports A, B, C, and D are organized into port pairs using a method that leverages all of the SAS
ports for system resiliency and consistency when cabling controller-to-stack connections in HA pair
configurations.
• Port pairs consist of a controller A or C SAS port and a controller B or D SAS port. A and C SAS ports
connect to the logical first shelf in a stack. B and D SAS ports connect to the logical last shelf in a stack.
• Port pairs use all SAS ports on each controller in your system. You increase system resiliency by
incorporating all SAS ports (on an HBA in a physical PCI slot [slot 1-N] and on board the controller [slot 0])
into port pairs. Do not exclude any SAS ports.
• Port pairs are identified and organized as follows:
1. List A ports and then C ports in sequence of slots (0,1, 2, 3, and so on).
For example: 1a, 2a, 3a, 1c, 2c, 3c
2. List B ports and then D ports in sequence of slots (0,1, 2, 3, and so on).
For example: 1b, 2b, 3b, 1d, 2d, 3d
3. Rewrite the D and B port list so that the first port in the list is moved to the end of the list.
For example:
Offsetting the order of the slots by one balances port pairs across multiple slots (physical PCI slots
and on board slots) when more than one slot of SAS ports is available; therefore, preventing a stack
from being cabled to a single SAS HBA.
4. Pair the A and C ports (listed in step 1) to the D and B ports (listed in step 2) in the order that they are
listed.
.
Chapter 7 SAS cabling rules
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