HP StorageWorks 64 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Envir - Page 121
Device Fan-Out Ratio: 10 to 1, FCP and FICON in a Single Fabric
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Planning Considerations for Fibre Channel Topologies 3 Device Fan-Out Ratio 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. 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. Device Fan-Out Ratio: 10 to 1 10,000 IOPS TM TM Interswitch Link Fabric Connection 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS 1,000 IOPS Figure 3-14 Device Fan-Out Ratio Performance Tuning When designing or tuning a fabric for performance, it is critical to understand application I/O characteristics so that: Planning Considerations for Fibre Channel Topologies 3-35