Dell PowerVault 51F (8P Fibre Channel Switch) - Manual (Page 47)

support.dell.com PowerVault 51F Topologies 2-1
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DELL CONFIDENTIAL - Preliminary 4/6/00
C H A P T E R 2
PowerVault 51F Topologies
This chapter discusses some key factors affecting fabric performance, including the
following:
•
Fabric elements
•
Sample fabric topologies
Fabric Elements
Each fabric is unique and the elements that determine the fabric’s structure include:
•
Class of frames in the fabric
•
Type of host adapters connected to the fabric
•
Bandwidth requirements supported by the fabric
•
Topology of the switches in the fabric
•
Requirements for redundancy and fault tolerance
Regardless of the topology used, the switch’s extremely low message latency mini-
mizes fabric message handling time that results in a high-performance fabric.
Routing Cost
All Inter Switch Links (ISLs) have a default cost of 1000. The cost of a path between
any two switches in the fabric is the sum of the costs of all ISLs. The switches that
comprise the fabric always choose the lowest cost path through the fabric to forward
frames from the source switch to the destination switch.
When constructing a multiswitch configuration, called a cascaded fabric, a frame
entering the fabric may pass through eight switches before exiting the fabric. The
switch does not enforce the eight-switch limit. It is your responsibility to ensure that
the seven-hop limit is not exceeded. The command uRouteShow provides informa-
tion regarding the cost of the shortest path to another switch from which you can
derive the number of hops. The cost should not exceed 7000 (7 x 1000).
A fabric using Dell switches in cascaded topologies should be configured to deliver
the required bandwidth and fault tolerance with all connections made within the
seven-hop maximum limit.