Solaris architecture specific (Solaris DDI)
A scsi_address structure defines the addressing components for a SCSI target device. The address of the target device is separated into two components: target number and logical unit number. The two addressing components are used to uniquely identify any type of SCSI device; however, most devices can be addressed with the target component of the address.
In the case where only the target component is used to address the device, the logical unit should be set to 0. If the SCSI target device supports logical units, then the HBA must interpret the logical units field of the data structure.
scsi_hba_tran_t *a_hba_tran; /* Transport vectors for the SCSI bus */ ushort_t a_target; /* SCSI target id */ uchar_t a_lun; /* SCSI logical unit */
a_hba_tran is a pointer to the controlling HBA's transport vector structure. The SCSA interface uses this field to pass any transport requests from the SCSI target device drivers to the HBA driver.
a_target is the target component of the SCSI address.
a_lun is the logical unit component of the SCSI address. The logical unit is used to further distinguish a SCSI target device that supports multiple logical units from one that does not. The makecom(9F) family of functions use the a_lun field to set the logical unit field in the SCSI CDB, for compatibility with SCSI-1.