NonStop S-Series Server Description Manual (G06.24+)

Introduction

HP NonStop S-Series Server Description Manual—520331-003

1-22

Multiple I/O Enclosures

When two processor enclosures are interconnected in a basic configuration (using a

single pair of SEBs), they can each support two I/O enclosures. The resulting six

system enclosures are connected as shown in Figure 1-12. In this case, the router

ports from the SEBs serve two functions: they interconnect the ServerNet fabrics in the

two processor enclosures, and they provide external I/O access to two I/O enclosures.

In Figure 1-12, smaller blocks represent logic that was shown in detail in previous

topics. For example, the entire internal I/O structure for processor cabinets, shown in

detail in Figure 1-8 on page 1-15, is represented by a pair of ServerNet adapter blocks

and a pair of blocks divided into four parts that represent the four internal ServerNet

addressable controllers (SACs).

The I/O enclosure logic, shown earlier in Figure 1-10 on page 1-19, is even further

miniaturized to show eight enclosures in Figure 1-12. The only router connections

actually shown are those for the external connections to the routers in the SEBs in the

processor enclosures. The remaining five connections of each router are as previously

shown: one for each side of the four available ServerNet adapters (middle stack) and

the fifth one for the ServerNet bus interface (SBI, not shown) that interfaces to the four

SACs that are on each multifunction I/O board (MFIOB). Those four SACs, for the

SCSI bus, Ethernet, and so on, are represented by the blocks in the lower left and right

corners of the I/O enclosures.

In operation, note that each processor has two paths (either X or Y) to access any SAC

(which includes the ServerNet adapters) anywhere in Figure 1-12. That is possible

because of the SEB-to-SEB connection between the two processor enclosures. Each

passage through a router is a “router hop.” The hop count can vary from one to four in

this configuration.

Also note that it is not possible to cross over between X paths and Y paths. No matter

how extensive the ServerNet structure grows, the ServerNet fabrics for X and Y remain

separate and independent. Both are in simultaneous use at all times. A failure of a

ServerNet link between routers (or between a router and a SAC) affects only that

portion of the fabric. The remainder of the fabric remains fully functional. Operating

system software detects such link failures and provides automatic rerouting through

the opposite fabric whenever necessary.

In Figure 1-12, the configuration shown has ServerNet adapters in the processor

enclosures. However, in your own computing environment, those ServerNet adapters

can be replaced with pairs of additional SEBs instead. Such a configuration provides

much more I/O capability, as illustrated next.

Note. For simplicity, Figure 1-12 and Figure 1-13 show six-port routers in association with the

processors, thus resembling the configuration shown in Figure 1-7 on page 1-14. As shown in

Figure 1-8 on page 1-15, other NonStop servers have seven implemented router ports (instead

of six) and use two of them (instead of just one) to service the four internal SACs.