Reference Guide

Managing Long-Distance Fabrics
∙ Long-distance fabrics overview............................................................................................................................................................................ 483
∙ Extended Fabrics device limitations....................................................................................................................................................................483
∙ Long-distance link modes........................................................................................................................................................................................484
∙ Configuring an extended ISL...................................................................................................................................................................................484
∙ Forward error correction on long-distance links..........................................................................................................................................486
Long-distance fabrics overview
The most effective configuration for implementing long-distance SAN fabrics is to deploy Fibre Channel switches at each location in the
SAN. Each switch handles local interconnectivity and multiplexes traffic across long-distance dark fiber or wave-length division
multiplexing (WDM) links, while the Brocade Extended Fabrics software enables SAN management over long distances.
Brocade Extended Fabrics is an optional licensed feature for Brocade SAN deployment over distances beyond 10 km. A Brocade
Extended Fabrics license is required before you can implement long-distance dynamic (LD) and long-distance static (LS) distance levels.
The LD and LS settings are necessary to achieve maximum performance results over inter-switch links (ISLs) that are greater than 10
km.
For details about obtaining and installing licensed features, refer to the
Fabric OS Software Licensing Guide .
The Extended Fabrics feature enables the following functionality:
∙ Fabric interconnectivity over Fibre Channel at longer distances
ISLs can use long-distance dark fiber connections to transfer data. Wavelength-division multiplexing, such as dense wavelength-division
multiplexing (DWDM), coarse wavelength-division multiplexing (CWDM), and time-division multiplexing (TDM), can be used to increase
the capacity of the links. As Fibre Channel speeds increase, the maximum distance decreases for each switch.
The Extended Fabrics feature extends the distance the ISLs can reach over an extended fiber. This extension is accomplished by
providing enough buffer credits on each side of the link to compensate for latency introduced by the extended distance.
∙ Simplified management over distance
Each device attached to the SAN appears as a local device, which simplifies deployment and administration.
∙ Optimized switch buffering
When Extended Fabrics is installed on gateway switches (with E_Port connectivity from one switch to another), the ISLs (E_Ports) are
configured with a large pool of buffer credits. The enhanced switch buffers help ensure that data transfer can occur at near-full
bandwidth to use the connection over the extended links efficiently. This efficiency ensures the highest possible performance on ISLs.
Extended Fabrics device limitations
Brocade recommends that you do not use the FC8-64 and FC16-64 port blades for long distance because of their limited buffers.
These blades do not support long-wavelength (LWL) fiber optics and only support limited distance. However, you can use the
portCfgLongDistance command to reserve frame buffers for the ports intended to be used in long-distance mode through DWDM.
There is a limited number of reserved buffers used for long distance for each blade. If some ports are configured in long-distance mode
and have buffers reserved for them, insufficient buffers may remain for the other ports. In this case, some of the remaining ports may
come up in degraded mode.
Brocade Fabric OS Administration Guide, 8.0.1
53-1004111-02 483