SAS topology
It is possible to support different topologies of SAS with the Model 106 enclosure.
There are two basic forms of expansion topology as shown in Figure 1 and Figure 2. One is a simple daisy chain of enclosures one after another in a chain. The other topology is a star configuration that has each expansion enclosure connected from the host (server attached JBOD configuration) or controller enclosure (EBOD configuration).
A third example provided in Figure 3, shows use of all SAS ports via the daisy chain cabling method.
SAS cabling methods
As you face the rear panel of the Model 106 enclosure, the left IOM/EBOD expander module slot is 1 and the right IOM/EBOD expander module slot is 0. See also Figure 1 for CRU slot index numbering for the enclosure rear panel. Green is used to show IOM/EBOD expander module 0 paths and blue is used to show IOM/EBOD expander module 1 paths for cabling the expansion enclosures shown in each cascade.
The above diagram shows Daisy chain cabling method.
The above diagram shows Star cabling method.
An advantage of the star configuration is that each expansion enclosure is only one additional expander or “hop” away from the initiator. This reduces delays in the SAS communication path. Those effects are small by measure. However, there are a limited number of expansion ports, so for larger topologies, some combination of the two approaches will be required. Figure 3 provides another daisy chain cabling example with all 12Gb/s SAS ports connected.
