Storage Area Networks For Dummies®

Chapter 5: Designing the SAN
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Server
Server
Server
Host boundary
edge switches
Storage boundary
core switches
Figure 5-26:
Storage
core-edge
topology.
Storage
Disk
storage
In Figure 5-26, you can see 8 16-port switches for a total of 128 ports available
in this fabric. There are 24 dedicated ISL ports, leaving a total of 104 ports
left over for servers and storage. You’ll also notice from Figure 5-26 that only
seven of the storage core ports are being used. Instead of connecting more
storage to those switches, you can connect more switches to those ports.
If you leave available ports for more storage, 8 ports are left on each switch
to add more switches: 2 × 8 switches at 16 ports each, minus the two
required ISL links (this leaves 14 ports per switch), gives you another 224
ports for server connections. One more way to increase your port count in
the core-edge design is to replace the core switches with larger, directorclass
switches. (See Figure 5-27.)
Using director-class switches at the core not only gives you many more
ports available but also makes the core switches more robust. Director-class
switches are usually more reliable and have many more ports available than
modular switches. The director switches need to be more reliable because
they have so many more ports. A failure of a director-class switch affects a
lot more servers than does the failure of a single 16-port switch.