SAN Design: March 29, 2001 3:18 pm
53-0001575-01 BROCADE Technical Note Page: 3 of 31
2.0 Fabric Topologies
This section explores a variety of fabric topologies and provides some specific network examples for SAN fabrics. Topologies fall into the
following general categories:
•Meshed Topology-- a network of switches that has at least one link to each adjacent switch. Fully meshed designs will have a
connection from each switch in the fabric to all other switches in the fabric. Other topologies are a specific instance of a mesh design.
•Star Topology-- central switch(es) with some or all ports used to connect to other switches; edge switches connect only to the center
switches
•Tier Architecture -- a switch hierarchy of two or more levels with inter switch connections that assume data paths go from one side
(hosts) to the other side (targets).
Each of these topologies has advantages and disadvantages. The SAN designer should be aware of the features and benefits of each design
when building a solution for a specific customer environment. Some advantages and disadvantages are detailed here:
Meshed Topology Designs
•Provide any-to-any connectivity for devices
•Good for designs where locality of data is know and hosts and targets can be located on the same switch but where some amount
of any-to-any connections are needed
•Provide for resiliency on switch failure with the fabric able to re-route traffic via other switches in the mesh
•Allows for expansion at the edges without disruption of the fabric and attached devices
•Allows for scaling in size as port count demands increase (see SAN building block in the sample configuration section)
•Host and storage devices can be placed anywhere in the fabric
Star Topology Designs
•Two hops maximum, consistent latency
•Multiple equal cost paths allowing for load sharing at time of configuration of fabric
•Easy to start small and scale
•Two paths through the core from edge switches allows for failover