Specifications

DATA CENTER BEST PRACTICES
SAN Design and Best Practices 39 of 84
Using EX_Ports and VEX_Ports
If an FCR architecture is indicated, an “X” port is needed. An “X” port is a generic reference for an EX_Port or a
VEX_Port. The only difference between an EX_Port and a VEX_Port is that the “V” indicates that it is FCIP-facing.
The same holds true for E_Ports and VE_Ports; VE_Ports are E_Ports that are FCIP-facing.
The best practice in an FC routed environment is to build an edge fabric to backbone to edge fabric (EBE)
topology. This provides isolation of fabric services in both edge fabrics. This architecture requires an EX_Port
from the Backbone to connect to an E_Port in the edge fabric, as shown in Figure 26. The backbone fabric will
continue to be exposed to faults in the WAN connection(s), but because its scope is limited by the VE_Ports
in each edge fabric, and since edge fabric services are not exposed to the backbone, it does not pose any
risk of disruption to the edge fabrics in terms of overrunning the CPUs or causing a fabric service to become
unavailable. The edge fabric services do not span the backbone.
fig27_SAN_Design
Edge
Fabric
E_Port E_Port VE_Port VE_Port EX_Port EX_Port
Edge
Fabric
IP
Cloud
Brocade
7800
Brocade
7800
Backbone
FCIP Tunnel
Isolated
Edge Fabric
Isolated
Edge Fabric
Figure 26. Edge-backbone-edge FCR architecture.
There may be cases in which an EBE topology cannot be accommodated; alternatively, the main production
fabric can be isolated from aberrant WAN behavior, while allowing the backup site to remain exposed. This
provides a greater degree of availability and less risk compared to not using FCR at all. This type of architecture
uses VEX_Ports that connect to a remote edge fabric. The important point to observe here is that the remote
edge fabric continues to be connected to the WAN, and the fabric services span the WAN all the way to the
EX_Port demarcation point. This means that the fabric services spanning the WAN are subject to disruption and
repeated reconvergence, which can result in an outage within the remote edge fabric. This may not be of great
concern if the remote edge fabric is not being used for production (but merely for backup), since such WAN
uctuations are not generally ongoing.
There are two topologies that you can build from remote edge fabrics. In the rst, as shown in Figure 27,
production devices are attached directly to the backbone. In the second, as shown in Figure 28, the backbone
connects to a local edge fabric. In both cases, the other side is connected to a remote edge fabric via a VEX_
Port. Also in both cases, the production fabrics are isolated from the WAN. Between the two architectures, the
second architecture with the edge fabric is recommended for higher scalability. The scalability of connecting
devices directly to the backbone is relatively limited.
fig28_SAN_Design
N_Port N_Port F_Port F_Port VE_Port VEX_Port
IP
Cloud
Brocade DCX
with FR8-24
Brocade DCX
with FX8-24
Backbone
Fabric
FCIP Tunnel
Isolated Remote Edge Fabric
Figure 27. Backbone-remote edge architecture.