HP StorageWorks Fabric OS 6.x administrator guide (5697-7344, March 2008)

Fabric OS 6.x administrator guide 369
Fabric considerations
Because the number of buffer credits available for use within each port group is limited, configuring buffer
credits for extended links may impact the performance of the other ports in the group used for core-to-edge
connections. Balance the number of long-distance ISL connections and core-to-edge ISL connections within
a switch. Configuring long-distance ISLs between core and edge switches is possible, but is not a
recommended practice.
With the exception of older switches and blades that use the Bloom ASIC, all switch ports provide
protection against buffer depletion through buffer limiting. A buffer-limited port reserves a minimum of
eight buffer credits, allowing the port to continue to operate rather than being disabled due to a lack of
buffers. The 8 buffer minimum allows 4 Gbps speeds over distances within most data centers.
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.
Long distance link initialization activation
VC translation link initialization (vc_translation_link_init), a parameter of the
portCfgLongDistance command, is enabled by default for long-distance links. To avoid inconsistency
in the fabric, make sure that this parameter is enabled on both ends of the link by entering the
portCfgLongDistance --vc_translation_link_init command. Specify 1 to activate long
distance link initialization sequence; specify 0 to deactivate this mode. When the command is run without
specifying a value, 1 is assigned automatically for the long-distance link in VC_RDY flow control;
otherwise, 0 is assigned. For a long-distance link not configured for ISL R_RDY mode, this parameter must
be set to 1; otherwise, it must be reset to 0.
Extended Fabrics device limitations
Extended Fabrics is normally not implemented on the following devices.
• The
400 Multi-protocol (MP) Router and the FR4-18i blade integrate two Gigabit Ethernet ports and sixteen
FC ports. The two Gigabit Ethernet ports provide SAN extension over IP networks using FCIP.
• The FC4-16IP blade integrates eight Gigabit Ethernet ports and eight FC ports. It is used to implement
the iSCSI Gateway Service. The Gigabit Ethernet ports are used to connect iSCSI initiators, and the FC
ports are used to connect to any device.
Configuring an extended ISL
Before configuring an extended ISL, ensure that the following conditions are met:
• Be sure that the ports on both ends of the ISL are operating at the same port speed, and can be
configured at the same distance level without compromising local switch performance.
• Use only qualified Brocade SFPs.
NOTE: A long-distance link also can be configured to be part of a trunk group. Two or more
long-distance links in a port group form a trunk group when they are configured for the same speed,
the same distance level, and their link distances are nearly equal. For information on trunking
concepts and configurations, refer to ”Administering ISL Trunking” on page 377.
• Use only qualified HP SFPs.
• For fabrics that contain B-Series 2Gb switches, contact HP support for details on which
parameters to set.
• For Fabric OS 3.x or 4.x, contact HP for details on which parameters to set.
1. Connect to the switch and log in as admin.
2. Enter the switchDisable command.