3 Device management
To provide connectivity between hosts and devices, it is necessary for the interface card to be recognized with an address on the connected Fibre Channel network.
SCSI bus configuration
The interface card provides the capability to reset SCSI buses during the interface card boot cycle. This allows the devices on a SCSI bus to be set to a known state. Configuration provides for the SCSI bus reset feature to be enabled or disabled.
The interface card negotiates for the maximum values for transfer rates and bandwidth on a SCSI bus. If an attached SCSI device does not allow the full rates, the interface card uses the best rate it can negotiate for that device. Negotiation is on a device specific basis, so the unit can support a mix of SCSI device types on the same SCSI bus.
FC port configuration
By default, the configuration of the FC port on the interface card is set to N_Port mode. For more information, see the Fibre Channel Configuration sections in ”Interface card management” on page 27 and ”Fibre Channel port configuration” on page 42.
FC arbitrated loop addressing
On a Fibre Channel Arbitrated Loop, each device appears as an Arbitrated Loop Physical Address
(AL_PA). To obtain an AL_PA, two addressing methods, called soft and hard addressing, can be used by the interface card. Soft addressing is the default setting. For hard addressing, the user specifies the AL_PA of the interface card.
Soft addressing
When acquiring a soft address, the interface card acquires the first available loop address, starting from address 01 and moving up the list of available AL_PAs in the chart from 01 to EF. In this mode, the interface card obtains an available address automatically and then participates on the FC loop, as long as there is at least one address available on the loop connected to the interface card. Fibre Channel supports up to 126 devices on an Arbitrated Loop.
Hard addressing
When acquiring a hard address, the interface card attempts to acquire the AL_PA value specified by the user in the configuration settings. If the desired address is not available at loop initialization time, the interface card comes up on the FC loop using an available soft address. This allows both the loop and the unit to continue to operate. An example of this scenario would be when another device on the Arbitrated Loop has acquired the same address as that configured on the interface card.
Hard addressing is recommended for FC Arbitrated Loop environments where it is important that the FC device addresses do not change. Device address changes can affect the mapping represented by the host operating system to the application, and have adverse effects. An example of this would be a tape library installation, where the application configuration requires fixed device identification for proper operation. Hard addressing ensures that the device identification to the application remains constant.
FC switched fabric addressing
When connected to a Fibre Channel switch, the interface card is identified to the switch as a unique device by the factory programmed World Wide Name (WWN) and the World Wide Port Names (WWPN), which are derived from the WWN.