PEX 8649, PCI Express Gen 2 Switch, 48 Lanes, 12 Ports

Applications

Suitable for host-centric as well as peer-to-peer traffic

patterns, the PEX 8649 can be configured for a wide

variety of form factors and applications.

Host Centric Fan-out

The PEX 8649, with its symmetric or asymmetric lane

configuration capability, allows user-specific tuning to a

variety of host-centric applications. Figure 6 shows a

server design where, in a quad or multi processor system,

users can assign endpoints/slots to CPU cores to distribute

the system load. The packets directed to different CPU

cores will go to different (user assigned) PEX 8649

upstream ports, allowing better queuing and load balancing

capability for higher performance. Conversely, the PEX

8649 can also be used in single-host mode to simply fan-

out to endpoints.

Figure 6. Host Centric Dual Upstream

Multi-Host Systems

In multi-host mode, the PEX 8649 can be shared by up to

four hosts in a system. By creating four virtual switches,

the PEX 8649 allows four hosts to fan-out to their

respective endpoints. This reduces the number of switches

required for fan-out, saving precious board space and

power consumption. In Figure 7, the PEX 8649 is being

shared by four different servers (hosts) with each server is

running its own applications (I/Os). The PEX 8649 assigns

the endpoints to the appropriate host and isolates them

from the other hosts.

I/O

I/O

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I/O

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PEX 8649

PEX 8649

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Figure 7. Multi-Host System

Host Failover

The PEX 8649 can also be utilized in applications where

host failover is required. In the below application (Figure

8), two hosts may be active simultaneously and controlling

their own domains while exchange status information

through doorbell registers or I

be programmed to trigger fail-over if the heartbeat

information is not provided. In the event of a failure, the

surviving device will reset the endpoints connected to the

failing CPU and enumerate them in its own domain

without impacting the operation of endpoints already in its

domain.

CPU

CPU

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x8

x4 & x8

Chipset

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PEX 8649

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CPU

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x8

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PEX 8649

x8s

Figure 8. Host Fail-Over

N+1 Fail-Over in Storage Systems

The PEX 8649’s Multi-Host feature can also be used to

develop storage array clusters where each host manages a

set of storage devices independent of others (Figure 9).

Users can designate one of the hosts as the failover-host

for all the other hosts while actively managing its own

endpoints. The failover-host will communicate with other

hosts for status/heartbeat information and execute a

failover event if/when it gets triggered.

© PLX Technology, www.plxtech.com

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5/14/2009, Version 1.1