AB378A Fibre Channel Mass Storage Adapter Installation Guide, December 2005

Fibre Channel Adapter Installation
Interpreting Hardware Paths
Chapter 1
16
NOTE Fibre Channel devices can connect to a Fabric using either Direct Fabric Attach or Public Loop.
Different devices may have different types of connections to the same Fabric, for example an
HBA may have a Direct Fabric Attach connection to the Fabric, while an array has a Public
Loop connection to the same Fabric. In other words, in a Fabric, the Fibre Channel Topology of
an HBA may be different from the Fibre Channel Topology of devices seen by that HBA.
Public Loop devices have an Arbitrated Loop Physical Address (AL_PA). The AL_PA usually
appears in the least significant byte of the device's N_Port ID. Direct Fabric Attach devices do
not have an AL_PA and the least significant byte of their N_Port ID is usually 0. This is
dependent on the switch implementation and not all switches adhere to this scheme.
Some switches allow devices in Private Loop mode to connect to a Fabric. In these situations,
the switch typically translates the private loop device as either a Public Loop or Direct Fabric
Attach device to the rest of the Fabric. The switch also typically translates the rest of the Fabric
as Private Loop devices to the Private Loop device.