Not just a big switch


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Users aren't just looking to FC directors to isolate SAN fabrics; they also want them to virtualize storage and ports. After years of stops and starts, virtualization technologies are finally gaining some momentum and moving to FC directors.

So far, Cisco's MDS 9500 series and Maxxan Systems Inc.'s MXV500 are the only FC directors that support storage virtualization. Cisco's Cache Services Module (CSM) line card and Maxxan's MXV500 are similar in that they support virtualization software based on network caching. Cisco supports the director blade version of IBM Corp.'s SAN Volume Controller and Maxxan supports FalconStor Software Inc.'s IPStor. Cisco's other line card, the Storage Services Module (SSM), supports virtualization applications that don't use network cache like EMC Corp.'s Invista and Incipient Inc.'s Network Storage Platform (NSP).

Even though the SSM supports virtualization, it comes configured with 32 1Gb/sec and 2Gb/sec FC ports, and can operate with or without virtualization enabled. Cisco prices it just slightly above the cost of its normal 32-port line card. The SSM module also supports Cisco's SANTap protocol, which can communicate with Kashya Inc. and Topio Inc. so their products can make copies of FC writes as FC packets pass through the director. This enables applications like data replication and continuous data protection at the fabric level without the need to deploy host server agents or use array-based tools.

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Server virtualization technologies like Linux partitions and VMware are also driving a major FC director virtualization technology, called N-Port ID Virtualization (NPIV), which all of the large director vendors are offering on their latest directors. NPIV solves the problem created when multiple server partitions log into the SAN using the same physical host bus adapter (HBA) card. NPIV lets FC directors dole out a unique port ID to each server instance. For example, in a configuration where eight logical Windows or Linux instances reside on the same physical hardware, each logical server instance can log into the FC director and get its own fabric ID. This allows the fabric to control and route the traffic from each Windows server instance to its allocated resources. The unique ID prevents all of the server instances behind an individual server HBA from having access to all of the resources reserved for a specific HBA.

FC directors are solidifying their position in the enterprise. Higher port line cards with configurable buffer credits and different options for aggregating ISLs allow directors to connect the lowest tiers of storage to the enterprise, and to connect remote and local SANs over high-throughput FC links. And with technologies like InterSAN routing and NPIV maturing, FC directors are well-positioned to meet today's, and tomorrow's, challenges.

This was first published in February 2006

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