Modular Fibre Channel products allow high-bandwidth scalability by connecting blades or line cards in slots with central switching components (crossbars or control processors) across a high-bandwidth backplane or midplane. Each vendor has unique terms for the part or parts used for these port and control components:

However, not all products are created equal — higher bandwidth provides more room for growth, something critical when considering the high bandwidth demands of virtualized servers, tape backup and trunks to other switches. As a result, some ports are more capable than others.

How does Brocade compare?

Brocade's DCX Backbone architecture provides more bandwidth than any other product in the industry. The Brocade DCX provides 256 Gbit/sec of usable bandwidth between each port blade and the core switching blades. On each of the eight (8) ports blades, up to thirty-two (32) full-speed 8 Gbit/sec devices and ISLs (or forty-eight (48) 4 Gbit/sec devices) can simulateously communicate across the backplane to the core switching blades for a total of 2048 Gbit/sec (2Tbits/sec) of backplane bandwidth. (Note that the DCX has two distinct CP blades and two distinct core switching blades.) Additionally, Brocade's exclusive local switching technology provides even more full-speed 8 Gbit/sec bandwidth for neighboring ports on the same blade, up to 384 Gbit/sec per blade for a total of 3 Tbit/sec of usable local switching bandwidth per chassis. In addition to the 3 Tbit/sec of core and local switching bandwidth, the DCX provides an additional 528 Gbit/sec of ICL connectivity to another DCX, the equivalent of 64 8 Gbit/sec ISLs. In other words, instead of 128 ports sacrificed for ISLs, 128 more devices can be attached to two DCXs connected by ICLs.

The Brocade 48000 provides 64 Gbit/sec of usable bandwidth between each port blade and the control processors. On each of the eight (8) ports blades, up to sixteen (16) full-speed 4 Gbit/sec devices and ISLs (or 32 2 Gbit/sec devices) can simulateously communicate across the backplane to the control processors for a total of 512 Gbit/sec of backplane bandwidth. Additionally, Brocade's exclusive local switching technology provides even more full-speed 4 Gbit/sec bandwidth for neighboring ports on the same blade, up to 192 Gbit/sec per blade. You can learn more about Brocade director design by reading the Brocade 48000 Architecture white paper and as can be seen in the online port and power calculator.

The Brocade M6140 provides approximately 8 Gbit/sec of usable bandwidth between port modules and crossbars. Each of the thirty-five (35) port modules has four ports which can support either 2 Gbit/sec or 4 Gbit/sec ports for a total of 280 Gbit/sec of crossbar bandwidth.

The Brocade Mi10000 can provide 64 Gbit/sec of usable port bandwidth between up to eight (8) line modules (LMQs) and up to four (4) switching modules (SWXs) for a total of 512 Gbit/sec of crossbar bandwidth.

The Cisco MDS 9513 provides 48 Gbit/sec of usable bandwidth between linecards and crossbars. On each of the 11 port modules, no more than twelve (12) full-speed 4 Gbit/sec devices or trunks can communicate across the crossbar. Even on the 24- and 48-port MDS linecards, only 12 ports of full-speed 4 Gbit/sec are available — on the 48-port linecard, when 12 ports are locked at 4Gb, the other 36 ports only have access to 3.2 Gbit/sec that the slot can provide.* While Cisco will claim the MDS is "8 Gb ready", there are no 8 Gbit/sec MDS linecards available. The Cisco director design has more components per linecard and an active midplane, as opposed to Brocade's efficient integrated ASIC architecture and passive backplane design. As a result, Cisco directors require considerably more power and generate much more heat.

Data flow within Brocade and Cisco products differs considerably.

At 64 Gbit/sec, the Brocade 48000 and Mi10000 have 33% more backplane bandwidth per slot than Cisco. At 256 Gbit/sec, the Brocade DCX has five (5) times the bandwidth per slot than the MDS 9513. In addition, the Brocade DCX and 48000 support local switching and is thus able to save that valuable bandwidth for data that must cross the backplane to get to another blade. In contrast, any time data enters a Cisco port, it always crosses the backplane and consumes backplane bandwidth even if traffic is local to the linecard or module.

This architectural difference has significant consequences. Whereas each Brocade ASIC can make forwarding decisions, the Cisco crossbar design requires that the forwarding ASIC confirm with the central arbitor on the supervisor before sending packets through the crossbar to the receiving ASIC even if ports are on the same linecard. Since Cisco only has 48 Gbit/sec between a line card and the crossbar, only 12 ports of 4 Gbit/sec can run simultaneously on any Cisco linecard. As an example, when 12 ports on the 48-port MDS linecard are locked at 4Gb, the remaining 36 ports will be severely oversubscribed -- 9 ports will have to share just 0.8 Gbit/sec of bandwidth.*. While all ports can be left to fight over the 51.2 Gbit/sec, the limits of the oversubscribed MDS architecture is readily apparent when SAN administrators have to decide when and where virtualized servers, tape backups and ISLs can be attached. This is not an issue with the Brocade DCX.

Note that Cisco will often double bandwidth numbers in a marketing effort to overcome their technical limitations. They will often reference the 48 Gbit/sec per slot in the 9513 as "96Gbit/sec" (and will sometimes double this again to count the 2nd unused crossbar). These "full duplex" or "cross-sectional" bandwidth measurements need be compared to the port speed in order to make equivalent measurements. However, no matter how many times you double the bandwidth number, the MDS 9513 supports just 12 full-speed 4 Gbit/sec ports per slot, and only 132 full-speed 4 Gbit/sec ports per chassis, a fraction of the 48 full-speed 4 Gbit/sec ports per slot and 384 full-speed 4 Gbit/sec ports in each DCX.