FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DC-TE, June 2003)

Planning Considerations for Fibre Channel Topologies
81SAN High Availability Planning Guide
■ Distance requirements — The distance between elements in a fabric affects
the type of optical port transceiver and cabling required. In addition, variables
such as the number of connections, grade of fiber-optic cable, device
restrictions, application restrictions, buffer-to-buffer credit limits, and
performance requirements can affect distance requirements. Consider the
following:
— If the distance between two fabric elements is less than 250 meters (at
2.125 Gbps), any port type (shortwave or longwave laser) and any
fiber-optic cable type (multimode or single-mode) can be used to create
an ISL connection. In this case, cost or port availability may be the
determining factor.
— If the distance between two fabric elements exceeds 300 meters (at 2.125
Gbps), only longwave laser ports and single-mode fiber-optic cable can be
used to create an ISL.
— Distance limitations can be increased by using multiple fabric elements.
Each director or switch retransmits received signals, thus performing a
repeater and multiplexer function. Distance limitations can also be
increased by using a variety of local area network (LAN), metropolitan
area network (MAN) or wide area network (WAN) extension
technologies.
Note: Variables such as the number of connections, grade of fiber-optic cable, device
restrictions, application restrictions, buffer-to-buffer credit limits, and performance
requirements can affect distance requirements.
■ Bandwidth — ISL connections can be used to increase the total bandwidth
available for data transfer between two directors or switches in a fabric.
Increasing the number of ISLs between elements increases the corresponding
total ISL bandwidth, but decreases the number of port connections available
to devices. Table 2 illustrates ISL transfer rate versus port availability for a
fabric consisting of two Director 2/64s.