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CHAPTER 1
Introduction to
the S-2500B
Linking Your SAN via SONET
Conventional storage area network (SAN) technology based on Fibre Channel (FC) is limited
in reach to 10 km or less. This is sufficient for most campus or single-location enterprise
applications. As storage needs increase, however, so too does the need to access this storage
over longer distances. Applications such as disaster recovery, dedicated tape backup at a
*
remote site, and data-center to data-center backup and sharing all exceed the 10 km limit.
In a typical SAN network based on FC communication protocol, FC F_Ports from the fabric
switch are connected to FC N_Ports such as disk drives and host bus adapters that make up the
SAN network. FC E_Ports are used to interconnect FC fabric switches. The 10 km limitation is
primarily due to the link level buffer-to-buffer credit mechanisms employed by FC fabric
devices.
The most effective possible means of increasing the distance between switches is to link them
through a dedicated fiber connection. However the installation costs of such a connection are
very high, particularly for distances of tens to hundreds of kilometers that are required by
many remote storage applications.
The most straightforward, practical means to increase the distance between switches is to
terminate them directly onto existing metropolitan area networks or wide area networks using
standard and easily transported protocols. Of the various choices of optical data transport,
SONET offers a number of clear advantages for extending an FC-based SAN. The LightSand
S-2500B Gateway has been optimized to make full use of these advantages for extending
storage area networking.
* For example, the Sound Practices recommendations from the Security and Exchange Commission (SEC) set the
minimum safe distance between primary and backup sites to be between 200 to 300 miles.
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