Controller-To-Stack Connection Rules - Lenovo DM120S Installation And Cabling Manual

Double-wide shelf-to-shelf connectivity
• Double-wide shelf-to-shelf connectivity is used in quad-pathed (quad-path HA and quad-path)
configurations.
• Double-wide shelf-to-shelf connectivity requires two cable connections between disk shelves in each
domain—domain A (IOM A) and domain B (IOM B). The first cable connection is cabled as standard shelf-
to-shelf connectivity (using IOM ports 3 and 1); the second cable connection is cabled as double-wide
shelf-to-shelf connectivity (using IOM ports 4 and 2).
From the logical first shelf to the logical last shelf in a stack, you connect IOM port 3 to the next shelf's
IOM port 1 in domain A and then domain B. From the logical first shelf to the logical last shelf in a stack,
you connect IOM port 4 to the next shelf's IOM port 2 in domain A and then domain B. (IOM ports cabled
as double-wide connectivity are shown with blue.)

Controller-to-stack connection rules

You can correctly cable the SAS connections from each controller to each stack in an HA pair configuration
by understanding that SAS disk shelves use software-based disk ownership, how controller ports A/C and B/
D are connected to stacks, how controller ports A/C and B/D are organized into port pairs, and how
DM3000x, DM5000x, or DM7000x ports 0b and 0a are connected to stacks.
SAS disk shelf software-based disk ownership rule
SAS disk shelves use software-based disk ownership (not hardware-based disk ownership). This means that
disk drive ownership is stored on the disk drive rather than it being determined by the topology of the storage
system's physical connections (as it is for hardware-based disk ownership). Specifically, disk drive
ownership is assigned by ONTAP (automatically or by CLI commands), not by how you cable the controller-
to-stack connections.
SAS disk shelves should never be cabled using the hardware-based disk ownership scheme.
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Chapter 7 SAS cabling rules
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