scsi_ctl.7 (2010 09)

s
scsi_ctl(7) scsi_ctl(7)
where component parts of the minor number are constructed as follows:
ii Two hexadecimal digits, identifying the controlling interface card by its "Instance" number.
The Instance value is displayed in ioscan (1M) output, under column
I for the "Interface"
hardware type.
t One hexadecimal digit identifying the drive (target) address.
l One hexadecimal digit identifying the logical unit number (LUN) within the device.
0 Hexadecimal digit zero, for the reserved portion of the minor of the minor number.
o Optional values as follows:
0 To perform Inquiry on open to to ensure the device exists (recommended); or
2 To inhibit Inquiry on open. Starting with HP-UX 11i v3, option 2 is deprecated. It is main-
tained for binary compatibility with existing applications that already set it. An Inquiry
command will actually be sent during an open, regardless of whether or not this option is
set.
SCSI Communication Parameters
HP-UX supports the SCSI device protocol on parallel SCSI interfaces, Fibre Channel interfaces, and
Serial Attached SCSI interfaces. The SCSI communication parameters described here might only apply
to certain SCSI interfaces and are noted as such in the descriptions.
SCSI communication parameters control features related to communication for three different scope lev-
els: bus (link), target, and logical unit number (LUN). Bus communication parameters apply to all tar-
gets connected to a specific bus. Target communication parameters apply to all LUNs associated with a
specific target. LUN communication parameters apply to a specific LUN. SCSI communication parame-
ters apply to all device drivers (both device-specific and
scsi_ctl).
At power-up and after being reset, all parallel SCSI devices and hosts communicate using asynchronous
data transfers. Asynchronous data transfers use request (REQ) and acknowledge (ACK) signaling. The
strict ordering of REQ and ACK signaling simplifies the communication protocol but limits I/O perfor-
mance. A SCSI target and host pair may agree to use synchronous data transfers to increase I/O perfor-
mance.
Synchronous data transfers improve I/O performance by lessening the ordering requirements on REQs
and ACKs. By allowing multiple outstanding REQs, signal propagation delays and temporary rate imbal-
ances are better tolerated. To make use of synchronous data transfers, a SCSI target and host must nego-
tiate to determine mutually acceptable maximum REQ-ACK-offset and data-transfer rate parameters.
The maximum REQ-ACK-offset parameter indicates the maximum allowable number of outstanding
REQs. The value zero is used to indicate asynchronous data transfer. Other values indicate synchronous
data transfer. The appropriate value is generally dependent on the size of the receive data FIFO. High
values tend to improve data transfer rates. The maximum data-transfer rate parameter indicates the
"burst" data transfer rate (minimum allowable time between successive synchronous data transfers). A
SCSI synchronous data transfer request (SDTR) message, used to initiate the negotiation process, is asso-
ciated with the processing of a SCSI command.
At power-up and after being reset, all parallel SCSI devices and hosts communicate using eight-bit data
transfers. A SCSI target and host pair may agree to use sixteen-bit (wide) data transfers to increase I/O
performance. To make use of wide data transfers, a SCSI target and host must negotiate to determine a
mutually acceptable data transfer width parameter. A SCSI wide data transfer request (WDTR) message,
used to initiate the negotiation process, is associated with the processing of a SCSI command.
Some SCSI devices are able to simultaneously manage multiple active commands. Such a device has a
command queue that holds commands for processing. Command queuing can improve I/O performance
by reducing the time spent by the device waiting for new commands from the host. Note that command
queuing might not improve I/O performance substantially for devices that support "read-ahead" and
"immediate-reporting" (see scsi_disk (7) and scsi_tape (7)). The SCSI device and host use command tags to
correctly manage these multiple simultaneously active commands. At all times when command queuing
is in effect, each active command being handled by a specific LUN has a unique command tag.
SCSI devices indicate their ability to support the special communication features described above in their
SCSI
INQUIRY command data. Normally the SCSI INQUIRY command data and negotiation protocols
allow hosts and devices to determine the optimal communication parameters so that I/O performance is
maximized.
2 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: September 2010