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Fibre Channel directors offer ways to connect disparate SANs, isolate data and devices within a fabric, and deliver different levels of throughput on the fly. Here's how the big three directors match up.
NO LONGER JUST A BIG BOX with lots of ports, the Fibre Channel (FC) director has become the cornerstone around which next-generation SANs will be built. As more organizations are faced with managing petabytes of storage, director-class switches are easing management tasks by isolating SANs within a single fabric, delivering a higher level of data protection, and parceling throughput to individual ports depending on changing application demands.
|Fibre Channel directors: Core components|
|Click here for a comprehensive list of Fibre Channel directors: Core components (PDF).|
Of course, some things never change: First and foremost, companies look to directors to provide rock-solid stability with high levels of availability, throughput and port count. In this vein, the passive backplanes that are used in Brocade Communications Systems Inc.'s SilkWorm 48000, Cisco Systems Inc.'s MDS 9509 and McData Corp.'s Intrepid 10000 (i10K) nearly eliminate the possibility of failures. Each of these models also supports at least 1Tb/sec of internal bandwidth in a single chassis and 384 FC ports in a single rack; Brocade and Cisco offer configurations that support up to 768 FC ports in a rack. But as some vendors pack more ports into their line cards to meet growing user capacity demands, they're using port oversubscription to do so.
Port oversubscription occurs when the amount of internal switching fabric bandwidth allocated to a switch port is less than the device connection speed at that port. For example, if a port on an FC switch has a connection speed of 2Gb/sec, but is unable to achieve a wire-rate of 2Gb/sec, then the port is said to be oversubscribed. As a result, administrators need to plan how and under what circumstances to deploy these high port-count line cards.
This was first published in February 2006