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Planning Considerations for Fibre Channel Topologies
3
Core-to-Edge
Fabric
McDATA Products in a SAN Environment - Planning Manual
3-16
A modified or partial-mesh fabric is similar to a full-mesh fabric, but
each switch does not have to be directly connected to every other
switch in the fabric. The fabric is still resilient to failure but does not
carry a cost premium for unused or redundant ISLs. In addition,
partial-mesh fabrics scale easier than full-mesh fabrics. Partial-mesh
fabrics are useful when designing a SAN backbone for which traffic
patterns between SAN islands connected to the backbone are well
known. If heavy traffic is expected between a pair of switches, the
switches are connected through at least one ISL; if minimal traffic is
expected, the switches are not connected.
In general, mesh fabrics can be difficult to scale without downtime.
The addition of switches or directors usually involves disconnecting
fabric devices and may involve disconnecting in-place ISLs. As a
result, full or partial-mesh fabrics are recommended for networks
that change infrequently or have well-established traffic patterns.
A core-to-edge fabric consists of one or more directors or switches
acting as core elements that are dedicated to connecting other
directors and switches (edge elements) in the fabric. Core directors
act as high-bandwidth routers with connectivity to edge fabric
elements.
Figure 3-10
illustrates the topology with two core directors
and fourteen edge directors and switches (2-by-14 topology).
Subject to large fabric design constraints, core-to-edge fabrics are easy
to scale through the addition of core elements. The topology offers
any-to-any device connectivity and evenly distributes traffic
bandwidth throughout the fabric. The topology provides the most
flexible architecture to address fabric performance, traffic locality,
data integrity, connectivity, and scalability requirements.
The simplest core-to edge fabric has two or more core switching
elements that may or may not be connected (simple or complex). In a
simple core topology as shown in
connected. In a complex core topology, core switches are connected.
The figure also illustrates a topology where the core is a full-mesh
fabric.
Figure
3-10, core switches are not
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