McDATA Sphereon 4300 Specifications download pdf (Page 118)

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McDATA Products in a SAN Environment - Planning Manual

Planning Considerations for Fibre Channel Topologies

Figure 3-13 Device Locality

Although it is possible to design a SAN that delivers sufficient ISL

bandwidth in a zero-locality environment, it is preferable to design

local, one-to-one connectivity for heavy-bandwidth applications such

as video server, seismic data processing, or medical 3D imaging.

When designing a core-to-edge fabric, servers and storage devices

that support such bandwidth-intensive applications should be

attached to core directors as Tier 1 devices. As a best practices policy

(assuming 1.0625 Gbps ISLs), devices that generate a sustained

output of 35 MBps or higher are candidates for Tier 1 connectivity.

FICON devices also must use Tier 1 connectivity. For additional

information, refer to FCP and FICON in a Single Fabric.

Device Fan-Out Ratio The output of most host devices is bursty in nature, most devices do

not sustain full-bandwidth output, and it is uncommon for the output

of multiple devices to peak simultaneously. These variations are why

multiple hosts can be serviced by a single storage port. This device

sharing leads to the concept of fan-out ratio.

Device fan-out ratio is defined as the storage or array port IOPS

divided by the attached host IOPS, rounded down to the nearest

whole number. A more simplistic definition for device fan out is the

ratio of host ports to a single storage port. Fan-out ratios are typically

device dependent. In general, the maximum device fan-out ratio

supported is 12 to 1. Figure 3-14 illustrates a fan-out ratio of 10 to 1.

High Device Locality

Low Device Locality

ISL

Low Traffic

High Traffic

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McDATA Sphereon 4300 Specifications Page 118