HP StorageWorks Fabric OS 5.0.0 Features Overview (AA-RW1NA-TE, May 2005)

Optional features24
Extended Fabrics
The Extended Fabrics feature extends the distance that interswitch links (ISLs) can reach.
As the distance between switches and the link speed increase, additional buffer-to-buffer
credits are required to maintain maximum performance. The number of credits reserved for a
port depends on the switch model and the extended ISL mode for which it is configured.
The following HP StorageWorks models each contain a port group called a quad:
• HP StorageWorks SAN Switch 2/8V
• HP StorageWorks SAN Switch 2/16V and 2/16N
• HP StorageWorks SAN Switch 2/32
• HP StorageWorks Core Switch 2/64
• HP StorageWorks SAN Director 2/128
A quad port group contains four ports and shares a common pool of credits.
Because the number of credits available for use within each port group is limited, configuring
ports for extended links on these models might cause other ports to become disabled if there
are not enough buffer credits available.
For the HP StorageWorks SAN Switch 4/32 model, each port group contains eight ports,
and buffer credits are shared among all ports on the switch. This design is called buffer-limited
port technology. This technology allows all ports to remain operational, even when extended
links are in use.
A buffer-limited port can come online with fewer buffer credits allocated than its configuration
specifies. This type of allocation allows the port to operate at a reduced bandwidth instead of
being disabled for lack of buffers. Buffer-limited operation is persistent across switch reboots or
power cycles.
NOTE: Long-distance connections can participate in trunking if the ISL Trunking license is
installed. For more information, refer to the next section, “ISL Trunking.”