FW V06.XX/HAFM SW V08.02.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DD-TE, July 2004)

Physical Planning Considerations
135SAN High Availability Planning Guide
Extended-Distance Ports
Through longwave laser transceivers and repeaters or dense wavelength division
multiplexing (DWDM) equipment, Directors and Edge Switches support Fibre
Channel data transmission distances of up to 100 km at 1 Gbps, or 50 km at 2
Gbps. The extended distance feature is enabled on a port-by-port basis by
activating the 10-100 km check box for a specified port on the Element Manager
application’s Configure Ports dialog box. This feature provides extended
distance support using Fibre Channel protocol only and does not support distance
extension using Fibre Channel over Internet Protocol (FCIP) conversion.
When a port is configured for extended distance operation, the buffer-to-buffer
credit (BB_Credit) value for the port is automatically set to 60. This value
provides sufficient buffering to handle frame processing for link distances up to
100 km. When a director or switch port is configured to support extended link
distances, the attached device (or attached fabric element) must also support
extended distance operation and be configured to use a higher BB_Credit value to
maintain link efficiency.
If the extended distance feature is enabled for a port that is not installed or does
not support extended distance operation, the configuration for the feature is
ignored. In addition, a director or switch port configured for extended distance
operation cannot transmit broadcast frames to other ports in a Fibre Channel
fabric.
High-Availability Considerations
To provide high device availability, critical servers, storage devices, or
applications should be connected to more than one fabric element (director or
switch) or to more than one fabric. To determine if dual-connection capability
exists for a device, refer to the associated device documentation. To provide high
fabric availability, consider the use of multiple fabric elements, multiple ISLs, or
redundant fabrics. Refer to “Fabric Availability” on page 105 for additional
information.
Plan to maintain unused (spare) director and switch ports if port connections must
be quickly moved and re-established after a failure. If an individual port or an
entire port card fails, optical transceivers or port cards can be removed and
replaced, spare port connections identified (through the Element Manager
application), and fiber-optic cables rerouted and reconnected while the director or
switch is operational.