FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Environment Planning Manual (620-000124-500, April 2005)

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Planning Considerations for Fibre Channel Topologies
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Planning Considerations for Fibre Channel Topologies
Fabric Performance
During the design phase of a Fibre Channel fabric, performance
requirements of the fabric and of component directors, fabric
switches, and devices must be identified and incorporated. An
effective fabric design can accommodate changes to performance
requirements and incorporate additional directors, switches, devices,
ISLs, and higher speed links with minimal impact to fabric operation.
Performance factors that affect fabric design include:
• Application input/output (I/O) requirements, both in Gbps and
I/Os per second (IOPS).
• Storage port fan-out.
• Hardware limits, including the maximum directors and switches
per fabric, maximum number of ISLs per director or switch, and
maximum hops between devices. For additional information,
refer to Fabric Topology Limits.
• Software limits, including the maximum number of fabric
elements managed by the SAN management application and the
maximum number of zones and zone members. For additional
information, refer to SAN Management Applications and
Configuring Zones.
I/O Requirements McDATA directors and fabric switches are designed with non-
blocking architecture; therefore any two switch ports can
communicate at the full Fibre Channel bandwidth of 1.0625, 2.1250,
or 10.2000 Gbps without impact to other switch ports. Because most
SAN-attached devices are not capable of generating I/O traffic at the
full bandwidth, there is little potential for congestion between two
devices attached through a single director or switch.
However, when multiple directors or switches are connected through
a fabric ISL that multiplexes traffic from several devices, significant
potential for congestion arises. To minimize congestion, factors such
as application I/O profiles, ISL oversubscription, and device locality
must be included in the fabric design.
Application I/O Profiles
Understanding application I/O characteristics is essential to SAN,
fabric, and ISL design. Factors that may affect application I/O
include: