Virtual TapeServer SCSI-to-FC Adapter User Manual

4-2
Chapter 4: Addressing and Logical Unit Management
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 VT5900-SA. Soft addressing is the default setting. For hard addressing, the user
specifies the AL_PA of the VT5900-SA.
Soft Addressing
When acquiring a soft address, the VT5900-SA 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. (See
Appendix C.) In this mode, the VT5900-SA 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 VT5900-SA. Fibre Channel supports up to 126 devices on an Arbitrated Loop.
Hard Addressing
When acquiring a hard address, the VT5900-SA 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 VT5900-SA 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 VT5900-
SA.
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 VT5900-SA is identified to the switch as a unique
device by the factory programmed World Wide Name (WWN).
Discovery
Discovery is a feature that makes it easy to display attached FC target devices and have them
mapped automatically on the host side for the bus/port in question.
There are also two discovery methods available—Manual Discovery and Auto Discovery.
Additionally, Auto Discovery can be set to occur after either reboot events (when the VT5900-SA