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SAS cabling rules

Disk shelves with IOM12 modules can be cabled in HA pair configurations by applying the SAS cabling rules: configuration rules, controller slot numbering rules, shelf-to-shelf connection rules, and controller-to-stack connection rules.

Note
The SAS cabling rules regarding controller slot numbering rules, shelf-to-shelf connection rules, and controller-to-stack connection rules described in this guide are the same rules that apply to all SAS disk shelves, whether they have IOM12, IOM6, or IOM3 modules. However, the information in this guide is specific to the unique characteristics of disk shelves with IOM12 modules and their use in supported configurations.

The SAS cabling rules regarding configuration rules described in this guide are specific to disk shelves with IOM12 modules.

The SAS cabling rules described in this guide balance SAS cabling between the on-board SAS ports and host bus adapter SAS ports to provide highly available storage controller configurations and meet the following goals:

  • Provide a single, easily understood universal algorithm for all SAS products and configurations
  • Yield the same physical cabling when generating the Bill of Materials (BOM), followed in the factory, and in the field
  • Are verifiable by configuration-checking software and tools
  • Provide maximum possible resilience to maintain availability and minimize the reliance on controller takeovers

You should avoid deviating from the rules; deviations might reduce reliability, universality, and commonality.

  • Configuration rules
    Disk shelves with IOM12 modules are supported in specific types of HA pair configurations.
  • Controller slot numbering rules
    For the purpose of applying cabling rules across all supported HA pairs configurations, a controller slot numbering convention is used.
  • Shelf-to-shelf connection rules
    When you have more than one disk shelf in a stack of disk shelves, they connect to each other through each SAS domain (IOM A and IOM B) using the applicable standard or double-wide shelf-to-shelf cabling. Your use of standard or double-wide shelf-to-shelf cabling depends on the configuration you have.
  • 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.