HP StorageWorks 2.128 SAN Director Switch - Manual (Page 163)

Fabric OS 5.x administrator guide 163
11 Administering extended fabrics
This chapter contains procedures for using the HP Extended Fabrics licensed feature, which extends the
distance that ISLs can reach. To use extended ISL modes, you must first purchase and install the Extended
Fabrics license. For details on obtaining and installing licensed features, see ” Maintaining licensed
features ” on page 26.
About extended link buffer allocation
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 on the extended ISL mode for which it is configured.
SAN Switch 2/8V, SAN Switch 2/16V, and SAN Switch 2/32, Core Switch
2/64, SAN Director 2/128, and 4/256 SAN Director (FC2-16 port blades)
For the SAN Switch 2/8V, SAN Switch 2/16V, SAN Switch 2/32, Core Switch 2/64, SAN Director
2/128, and 4/256 SAN Director using FC2-16 port blades, each port group contains four ports and
uses 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 example:
• If two 2-Gb/second ports in a group are configured for L1 mode, each is allocated sufficient
buffer-to-buffer credits to cause the other two ports in the group to become disabled.
• A port connected to a device that is in loopback mode might become disabled for lack of buffers if
another port in that group is set to L2 mode.
See Chapter 5, ” Configuring Core Switch 2/64, SAN Director 2/128, and 4/256 SAN Director ” for
details about port blade nomenclature.
Brocade 4Gb SAN Switch for HP p-Class BladeSystem, SAN Switch 4/32, and
4/256 SAN Director (FC4-16 and FC4-32 port blades)
For the SAN Switch 4/32 and 4/256 SAN Director using FC4-16 and FC4-32 port blades, buffer credits
are used by all ports on chip. Buffer-limited port technology allows all ports to remain operational, even
when extended links are in use.
For the Brocade 4Gb SAN Switch for HP p-Class BladeSystem, buffer credits are available to all ports on
the chip.
A buffer-limited port can come online with fewer buffer credits allocated than its configuration specifies,
allowing it to operate at a reduced bandwidth instead of being disabled for lack of buffers.
Buffer-limited operation is supported for the L0 and LD extended ISL modes only, and is persistent across
reboots, switch disabling and enabling, and port disabling and enabling.
Fabric considerations
Consider these items that affect the fabric when you configure extended ISLs:
• The extended link configuration mode, L2, can reach 100 km at a speed of 2 Gb/sec between Fabric
OS 4.x switches. However, it supports up to 60 km only if the link is established between Fabric OS
3.x and 4.x switches.
• The standard distance and LD ISL modes cannot be enabled at the same time.
• Balance the number of LD ISL connections and core-to-edge ISL connections within a switch.
Configuring LD ISLs between core and edge switches is possible, but HP does not recommend it.