HP StorageWorks 2/140 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN En - Page 120

Planning Considerations for Fibre Channel Topologies 3 • Upgrade the existing ISL - Fabric element software, firmware, and hardware can be upgraded to support a 2.1250 or 10.2000 Gbps bandwidth traffic load between fabric elements. A 2.1250 or 10.2000 Gbps ISL is sufficient to support the bandwidth of both NT servers operating at peak load. • Deliberately employ ISL oversubscription - SANs are expected to function well, even with oversubscribed ISLs. Device I/O is typically bursty, few devices operate at peak load for a significant length of time, and device loads seldom peak simultaneously. As a result, ISL bandwidth is usually not fully allocated, even for an oversubscribed link. An enterprise can realize significant cost savings by deliberately designing a SAN with oversubscribed ISLs that provide connectivity for noncritical applications. Device Locality Devices that communicate with each other through the same director or switch have high locality. Devices that must communicate with each other through one or more ISLs have low locality. Part (A) of Figure 3-13 illustrates high device locality with little ISL traffic. Part (B) of Figure 3-13 illustrates low device locality. High Device Locality A Low Device Locality B Low Traffic TM TM ISL High Traffic TM TM ISL 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. 3-34 McDATA Products in a SAN Environment - Planning Manual