General SAS cabling rules

You need to know the general SAS cabling rules governing supported configurations, cables, and SAS port connections on the disk shelves.

All HA pair configurations must use multipath HA, with the following exceptions:
- N3400 systems use single-path HA.
- N3240 systems with no external SAS storage can use single-path HA, which requires no external cabling.
  However, the recommended configuration is to enable multipath HA for the internal disks by connecting the SAS ports of one controller module to the SAS ports of the partner.
  
  Note: A multipath HA configuration having external shelves requires two ports on each controller for each stack of disk shelves. Even if the stack consists of one disk shelf, two ports on each controller are required.
All single-controller configurations must use dual-path, with the following exceptions:
- N3400 systems use single-path.
- N3240 systems have the internal disks cabled as single-path, but the system can use either single-path or dual-path connectivity to the external shelves; both are supported.
  Dual-path provides greater resiliency, but when dual-path is used, Data ONTAP 8.1.x issues occasional warnings to the console because mixed paths are detected. To avoid the warnings, single-path connections to the external SAS storage are a supported option in these configurations.
The SAS cables can be SAS copper, SAS optical, or a mix depending on whether or not your system meets the requirements for using the type of cable.
If you are using a mix of SAS copper cables and SAS optical cables, the following rules apply:
- Shelf-to-shelf connections in a stack must be all SAS copper cables or all SAS optical cables.
- If the shelf-to-shelf connections are SAS optical cables, the shelf-to-controller connections to that stack must also be SAS optical cables.
- If the shelf-to-shelf connections are SAS copper cables, the shelf-to-controller connections to that stack can be SAS optical cables or SAS copper cables.
The cable QSFP connector end connects to a disk shelf or a SAS port on a controller.
The SAS cable QSFP connectors are keyed; when oriented correctly into a SAS port, the QSFP connector clicks into place and the disk shelf SAS port LNK LED illuminates green. Do not force a connector into a port.

The following illustration shows a QSFP connector:
Note: The QSFP connector shown has a pull tab for releasing the connector from a SAS port; however, QSFP connectors can have a different release mechanism.
Disk shelves connected with SAS optical cables require a version of disk shelf firmware that supports SAS optical cables.
Best practice is to update all disk shelves in the storage system with the latest version of disk shelf firmware.
Note: Do not revert disk shelf firmware to a version that does not support SAS optical cables.
SAS optical multimode QSFP-to-QSFP cables can be used for controller-to-shelf and shelf-to-shelf connections, and are available in lengths up to 50 meters.
If you are using SAS optical multimode MPO cables with MPO QSFP modules, the following parameters apply:
- You can use these cables for controller-to-shelf and shelf-to-shelf connections.
- The length of a single cable cannot exceed 150 meters for OM4 and 100 meters for OM3.
- The total end-to-end path (sum of point-to-point paths from the controller to the last shelf) cannot exceed 510 meters.
  The total path includes the set of breakout cables, patch panels, and inter-panel cables.
If you are using SAS optical multimode breakout cables, the following parameters apply:
- You can use these cables for controller-to-shelf and shelf-to-shelf connections.
  If you use multimode breakout cables for a shelf-to-shelf connection, you can only use it once within a stack of disk shelves. You must use SAS optical multimode QSFP-to-QSFP or MPO cables with MPO QSFP modules to connect the remaining shelf-to-shelf connections.
- The point-to-point (QSFP-to-QSFP) path of any multimode cable cannot exceed 150 meters for OM4 and 100 meters for OM3.
  The path includes the set of breakout cables, patch panels, and inter-panel cables.
- The total end-to-end path (sum of point-to-point paths from the controller to the last shelf) cannot exceed 510 meters.
  The total path includes the set of breakout cables, patch panels, and inter-panel cables.
- Up to one pair of patch panels can be used in a path.
- You need to supply the patch panels and inter-panel cables.
  The inter-panel cables must be the same mode as the SAS optical breakout cable: multimode.
- You received a set of QSFP-to-MPO cable modules with each set of SAS optical breakout cables, which you must attach to the MPO end of each SAS optical breakout cable.
  The breakout cables have SC, LC, or MTRJ connectors on the opposite end, which connect to a patch panel.
- You must connect all eight (four pairs) of the SC, LC, or MTRJ breakout connectors to the patch panel.
QSFP-to-mini-SAS copper cables are used for N3600 configurations only, and connect disk shelves to the dual-port mini-SAS HBAs on the controller.
The following illustration shows the QSFP-to-mini-SAS cable connectors:
SAS ports on the disk shelf are designated by a square or circle symbol.

Square ports are always cabled to circle ports, and circle ports are always cabled to square ports. Never cable square ports to square ports or circle ports to circle ports. The following illustration shows square and circle port labeling on an IOM.