Fabric OS Administrator’s Guide 441
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Chapter
20

Managing Long Distance Fabrics

In this chapter
•Long distance fabrics overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
•Extended Fabrics device limitations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
•Long distance link modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
•Configuring an extended ISL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
•Buffer credit management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
•Buffer credit recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453

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 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 distance 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 on obtaining and installing licensed features, see Chapter 16, “Administering
Licensing”. The Extended Fabrics feature enables the following:
•Fabric interconnectivity over Fibre Channel at longer distances
ISLs can use long distance dark fiber connections to transfer data. Wave division multiplexing,
such as DWDM (Dense Wave Division Multiplexing), CWDM (Coarse Wave Division
Multiplexing), and TDM (Time Division Multiplexing), 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 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, an approach that simplifies
deployment and administration.
•Optimized switch buffering
When Extended Fabrics is installed on gateway switches (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 efficiently
utilize the connection over the extended links. This ensures the highest possible performance
on ISLs.