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N1200-320 4Gb Network Storage Router user and service guide 23
3 Device management
To provide connectivity between hosts and devices, it is necessary for the network storage router to be
recognized with an address on the connected Fibre Channel network.
SCSI bus configuration
The network storage router provides the capability to reset SCSI buses during the network storage router
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 network storage router 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 network storage router 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 network storage router is set to N_Port mode. For more
information, see the Fibre Channel Configuration sections in ”N1200-320 4Gb Network Storage Router
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 network storage router. Soft addressing is the default setting. For hard addressing, the user specifies
the AL_PA of the network storage router.
Soft addressing
When acquiring a soft address, the network storage router 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 network storage router 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 network storage
router. Fibre Channel supports up to 126 devices on an Arbitrated Loop.
Hard addressing
When acquiring a hard address, the network storage router 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 network storage router 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 network storage router.
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 network storage router 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.