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Planning Considerations for Fibre Channel Topologies
3
McDATA Products in a SAN Environment - Planning Manual
3-34
•
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
(B) of
Figure 3-13
High Device Locality
Low Traffic
Device Locality
Figure 3-13
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.
illustrates high device locality with little ISL traffic. Part
illustrates low device locality.
A
ISL
Low Device Locality
High Traffic
ISL
B
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