NonStop S-Series Server Description Manual (G06.27+)

Introduction

HP NonStop S-Series Server Description Manual—520331-004

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Modular I/O

Up to this point, the I/O topologies have considered only configurations that use I/O

enclosures of the same form factor as processor enclosures. One type of enclosure

can be converted to the other type. However, an entirely different I/O topology is also

available that differs significantly from that provided by connection through the

multifunction boards (MFIOBs) in I/O enclosures, that of modular I/O. (For

comparison, refer to Figure 1-10 on page 1-19.) Modular I/O uses different cabinetry

and architecture, and is described here and in the next three topics.

In addition to architectural differences, modular I/O uses different physical packaging.

For example, whereas the I/O enclosure physically stands on the floor or on top of

another enclosure and has its own front and back doors, the equivalent modular I/O

enclosure mounts inside a cabinet that provides standard 19-inch rack mount rails.

That external cabinet, which provides the front and back doors, is much larger than the

I/O enclosures previously described and has a totally different appearance. It can

contain a variable number of modular I/O enclosures.

The primary design intent of modular I/O is to provide extremely high bandwidth

access to a large array of storage and communication devices. Secondarily, modular

I/O provides for increased fault tolerance through fault isolation to smaller module

components and for easy replacement of those components. Module components can

be added online, thus making it possible to expand the I/O system with minimal effort.

Figure 1-20 illustrates how I/O modules fit into the NonStop server architecture. As

indicated, each module primarily consists of a ServerNet switch and five slots for

ServerNet adapters. The figure assumes that Fibre Channel ServerNet adapters

(FCSAs) are installed in those slots. However, other ServerNet adapters that have the

appropriate form factor, such as Ethernet adapters (G4SA, for example), can be

installed here.

ServerNet switches are always paired between two I/O modules. Although it might

appear that one module is accessed only through the X fabric and the other is

accessed only through the Y fabric, there is actually a cross coupling between the two

modules so that all ten ServerNet adapters in the two modules are accessed through

both X and Y fabrics. This arrangement is primarily for packaging efficiency, and the

cross coupling occurs through backplane connections in the enclosure.

Two 12-port routers are used in each ServerNet switch to enable routing of ServerNet

messages to and from all ten ServerNet adapter slots.

Fibre Channel ServerNet adapters provide two ports for external connection, each

controlled by individual ServerNet addressable controllers (SACs). This feature adds

connection capacity to very large external disk arrays such as the Enterprise Storage

System (ESS).