Overview of the configuration definitions

A host operating system definition consists of multiple fields. The preceding example attempts to show the primary fields that are required to define FCP devices in a host operating system. It specifies two logical units for one target device and one logical unit for another target device. The first field shown is the device number (for example, 0x1200), which is the same device number specified in the IOCP definition. The next field shown is the worldwide port number, identifying the Fibre Channel port of the SCSI target device (for example, 0x345adf…). The final field shown is the logical unit number (for example, 0x4209… and 0x420b…).

The IOCP definition consists of the FCP channel path, a control unit, which is only necessary so that devices can be defined, and a device. The device 1200 is associated with a subchannel in the logical channel subsystem (CSS).

A host application issues an I/O request. The SCSI/FCP stack gets the CSS subchannel number for the device number (1200) and packages the FCP I/O operation into a format acceptable for QDIO operations and passes it to the QDIO driver. The QDIO driver uses queues associated with the subchannel for device 1200 and performs the QDIO operation to the FCP channel adapter. The FCP channel performs the Fibre Channel Protocol operation with the correct destination logical unit (LUN) using the correct Fibre Channel port of the SCSI target device.