Cisco Cisco MDS 9500 Series Supervisor-2 Module Libro blanco

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As storage requirements continued to grow exponentially, the need to optimize storage usage by way of consolidation and better utilization

became necessary as a method to reduce overall total cost of ownership (TCO). This growth has led to the need for more scalable and flexible

SAN topologies to meet increasing storage requirements and increasing performance requirements of computing platforms.

Principles of SAN Design

The underlying principles of SAN design are relatively straightforward: plan a network topology that can handle the number of ports necessary now

and into the future; design a network topology with a given end-to-end performance and throughput level in mind, taking into account any physical

requirements of a design (for example, whether the data center is or will in the future be located on multiple floors of a building or in multiple

buildings or locations); and provide the necessary connectivity with remote data centers to handle the business requirements of business continuity

and disaster recovery.

These underlying principles fall into five general categories:

•

Port density and topology requirements—Number of ports required now and in the future

•

Device performance and oversubscription ratios—Determination of what is acceptable and what is unavoidable

•

Traffic management—Preferential routing or resource allocation

•

Fault isolation—Consolidation while maintaining isolation

•

Control plane scalability—Reduced routing complexity

Port Density and Topology Requirements

The single most important factor in determining the most suitable SAN design is determining the number of end ports—both now and over

the anticipated lifespan of the design. As an example, the design for a SAN that will handle a network with 100 end ports will be very different

from the design for a SAN that has to handle a network with 1500 end ports.

From a design standpoint, it is typically better to overestimate the port count requirements than to underestimate them. Designing for a 1500-port

SAN does not necessarily imply that 1500 ports need to be purchased initially, or even ever at all. It is about helping ensure that a design remains

functional if that number of ports is attained, rather than later finding the design is unworkable. As a minimum, the lifespan for any design should

encompass the depreciation schedule for equipment, typically three years or more. Preferably, a design should last longer than this, because

redesigning and reengineering a network topology become both more time-consuming and more difficult as the number of devices on a SAN

expands.

Where existing SAN infrastructure is present, determining the approximate port count requirements is not difficult. You can use the current number

of end-port devices and the increase in number of devices during the previous 6, 12, and 18 months as rough guidelines for the projected growth in

number of end-port devices in the future.

For new environments, it is more difficult to determine future port-count growth requirements, but once again, it is not difficult to plan based on

an estimate of the immediate server connectivity requirements, coupled with an estimated growth rate of 30 percent per year.

A design should also consider physical space requirements. For example, is the data center all on one floor? Is it all in one building? Is there a desire

to use lower-cost connectivity options such as iSCSI for servers with minimal I/O requirements? Do you want to use IP SAN extension for disaster

recovery connectivity? Any design should also consider increases in future port speeds, protocols, and densities. Although it is difficult to predict

future requirements and capabilities, unused module slots in switches that have a proven investment protection record open the possibility to future

expansion.