Support for Queuing

For a definition of tagged queuing, refer to the SCSI-2 specification. To support tagged queuing, first check the scsi_options flag SCSI_OPTIONS_TAG to see if tagged queuing is enabled globally. Next, check to see if the target is a SCSI-2 device and whether it has tagged queuing enabled. If this is all true, attempt to enable tagged queuing by using scsi_ifsetcap(9F).

If tagged queuing fails, you can attempt to set untagged queuing. In this mode, you submit as many commands as you think necessary or optimal to the host adapter driver. Then the host adapter queues the commands to the target one at a time (as opposed to tagged queuing, where the host adapter submits as many commands as it can until the target indicates that the queue is full).