Graphics Fan-out Switch
Dual Fabric Model
The number and variety of PCI Express native-mode devices
is growing quickly. The devices such as graphics cards are
expected to become mainstream very rapidly. As that happens,
it will be necessary to take a wide (x16) graphics port on the
root complex device and fan it out to four x4 or two x8 ports.
High performance communications, storage, and blade
server systems often require more reliability than a single host
system provides. For these high availability systems, all
single points of failure must be eliminated. The ExpressLane
PEX 8532 can offer this additional level of redundancy by
linking together 2 switch fabric cards in a dual-star topology.
Figure 5 shows an example of such a system. In this system,
both the host and fabric are on separate cards, and both can be
active simultaneously. The unique non-transparency feature
of the PEX 8532 is used to allow one fabric/host card to be the
primary and the other to be the secondary.
This approach can be used to provide more than two active
processing nodes. It is straightforward to create a generalized
multiprocessor system with smaller ExpressLane switches on
each card in non-transparent mode, and several PEX 8532
fabric cards to provide the fabric backbone.
Figure 3. Graphics Fan-out
Dual Host Model
The ExpressLane PEX 8532 supports applications requiring
dual host, host failover, and load-sharing applications
through the non-transparency feature. Figure 4 illustrates a
dual host system using an intelligent adapter card.
Figure 5. Dual Host & Fabric Usage
Switch Fabric Module
The ExpressLane PEX 8532 can also be used in Blade Server
switch fabric applications. Figure 6 illustrate the use of PEX
8532 in a Benes Switch configuration. The non-transparency
and peer-to-peer functions of PEX 8532 enable use of fewer
total switching elements and less hops from source to
destination.
Figure 4. Dual Host Usage
In this figure, the primary CPU (on the right) is the active
host; it configures and enumerates the system, and handles
interrupts and error conditions. If the primary host ceases
proper operation, the secondary host takes over the system.
The PEX 8532 can dynamically re-assign both the upstream
port (from primary to secondary) and the non-transparent
port (from the secondary to the primary), and allow the system
to continue operation.
Figure 6. Benes Switch Fabric
PLX [ PLX TECHNOLOGY ]
