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One of the key strategies when consolidating storage is to move toward larger switches and directors, reducing the total number of switches in the SAN. Besides simplifying switch management, fewer switches reduce the number of inter-switch link (ISL) data transfers and, as a result, decrease the debilitating impact of ISL bottlenecks.
There are two options when moving toward larger switches: Deploy relatively inexpensive high-port count switches such as Brocade's SilkWorm 4900 and QLogic Corp.'s SANbox 5200 and 5600, which scale up to 64 ports; or move to director-class switches. The 64-port switches typically come in a stackable form factor and aren't designed with the redundancy features of directors; however, if deployed in pairs, they constitute a high-availability switching solution that's especially attractive for smaller and midsized SANs requiring fewer than 64 ports.
For SANs that require the highest level of redundancy, director-level switches are the ideal consolidation platform. They're available with up to 512 4Gb/sec FC ports and, with an aggregate backplane capacity of more than 1Tb/sec, are equipped to cope with the most demanding switching needs. With a passive backplane, redundant blades, switching processors, fans and power supplies, they display the highest level of redundancy, eliminating all single points of failure. But a director's high availability, performance and scalability also make it the most expensive
Although a high-port aggregation switching solution will be part of most consolidation projects, especially to beef up the SAN core, existing switches will be redeployed rather than replaced in most cases. Legacy switches are typically moved further away from the core toward the edge, where they perform less mission-critical switching chores, connecting back to the core for inter-switch data transfers.
Repurposing or combining multiple smaller switches within a single SAN has become a viable approach as a result of enhancements in FC switching equipment. The biggest concerns with connecting isolated SANs have been problems such as rogue apps in one SAN affecting performance and availability in other SANs; FC is a basic Layer 2 protocol that doesn't have domain-isolation capabilities. Fortunately, today's FC switches, routers and directors provide features that address these concerns.
This was first published in December 2006