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Fibre Channel director face-off: Brocade vs. Cisco

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Both the 7500 router and FR4-18i Director Blade support a special type of E_Port for connecting different fabrics called an EX_Port. This allows Brocade to introduce its Fibre Channel Routing (FCR) feature into these two devices that allow different LSANs to communicate with one another.

FCR creates a virtualized switch called a "translate domain," which imports all of the nodes of the edge fabric. Resources are then accessed between different edge fabrics by creating a zone name starting with "LSAN_" that contains the port WWN of the nodes that will access each other. Brocade's FCR recognizes these new LSAN zones in the respective LSANs, automatically creates the appropriate routes and then allows communication between selected nodes in the two zones.

Brocade more fully preserves admins' control in separate and remote SAN islands by eliminating the need for a superuser. Admins of each remote SAN island or logical SAN first create an LSAN zone containing the nodes to be shared between LSANs. If an LSAN zone is created in only one LSAN, members defined in the zone aren't shared across LSANs by the FCR. This allows firms to preserve existing political boundaries and gain consolidation benefits.

Cost and complexity
As more services are added to the fabric, costs and management complexity increase. Costs may rise because each new service requires the addition of the appropriate switch to the fabric or director blade to the FC director.

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Because each new service introduces additional hops into the fabric, it may be prudent to add only one or two fabric services at a time.

Deepak Munjal, Cisco's data center solutions senior marketing manager, says some of the different fabric services will eventually move off switches and blades and become part of the MDS 9513's SAN-OS. Specialized ASICs on every FC port will eventually take over the processing for each service and let users select which services they want to offer to each app on a port-by-port basis. Munjal says cost and demand will drive these changes, but "it is not realistic to do this [now] since the price of putting an ASIC on every port is still not affordable."

It took three to five years for encryption to move from an appliance to a chip that sits on a router port in Ethernet networks, says Munjal. "Fabric services will likely follow the same path," he adds.

Port preservation 
The growth of blade servers creates a problem for FC directors: port preservation. A fully populated IBM Corp. BladeCenter Chassis can use up to 28 FC director ports assuming two paths; a Hewlett-Packard Co. BladeSystem c-Class can consume up to 32 FC director ports, again assuming redundant paths. In addition to using up ports, blade servers often can't use the bandwidth available to them on FC director ports.

To mitigate these issues, Brocade and Cisco offer blade switches that act as gateways from the blade servers to the FC director. Blade servers connect to these gateways as they normally would to an FC switch with an N_Port login. However, the switch connects to the FC director and presents itself as an N_Port or host ports instead of as an E_Port as FC switches normally do.

This was first published in August 2007

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