PEX 8649, PCI Express Gen 2 Switch, 48 Lanes, 12 Ports
Applications
CPU
CPU
CPU
CPU
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.
Chip
Set
Chip
Set
Chip
Set
Chip
Set
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.
PEX 8649
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
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
2
C interface. The devices can
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
CPU
CPU
CPU
CPU
CPU
CPU
Chipset
x8
Chipset
x8
x8s
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.
PEX 8649
Endpoint
Endpoint
Endpoint
PEX 8649
Endpoint
Endpoint
Endpoint
x4 & x8
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.
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5/14/2009, Version 1.1
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