HP-UX Reference (11i v2 07/12) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

s
scsi_ctl(7) scsi_ctl(7)
NAME
scsi_ctl - SCSI pass-through driver
DESCRIPTION
SCSI devices are controlled by a device-specific driver, when one exists. Device-specific drivers, such as
those for SCSI direct access (disk) and sequential access (tape) devices, coordinate device and driver states
to accomplish correct logical device behavior. The
scsi_ctl pass-through driver enables use of SCSI
devices and commands not normally supported by these device-specific drivers.
Depending on the minor number, a successful
open() call by scsi_ctl might or might not require the
device exist and respond to a SCSI Inquiry command. Once open,
ioctl() calls can be used to change
SCSI communication parameters or attempt SCSI commands and other SCSI operations. Since
scsi_ctl does not attempt to logically understand the target device,
read() and write() calls are
not supported.
Except where noted, the ioctls described here are available through all SCSI device drivers (including
device-specific drivers). All
reserved fields in the data structures associated with these ioctls must be
zero-filled.
Special Device File Minor Number
The scsi_ctl driver is the preferred method to perform the SIOC_IO ioctl, rather than going through a
device-specific driver (such as sdisk). To do this, you must create the device special file for
scsi_ctl.
Use mknod(1M), substituting the values in the minor number as noted:
/usr/sbin/mknod name c 203 0x
iitl0o
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 reserved portion of the minor number.
o Optional values as follows: 0 to perform Inquiry on open to ensure the device exists (recom-
mended); or 2 to inhibit Inquiry on open.
SCSI Communication Parameters
HP-UX supports the SCSI device protocol on parallel SCSI interfaces and Fibre Channel 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 levels:
bus (link), target, and logical unit number (LUN). Bus communication parameters apply to all targets con-
nected to a specific bus. Target communication parameters apply to all LUNs associated with a specific tar-
get. LUN communication parameters apply to a specific LUN. SCSI communication parameters 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
imbalances are better tolerated. To make use of synchronous data transfers, a SCSI target and host must
negotiate 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 synchro-
nous data transfer request (SDTR) message, used to initiate the negotiation process, is associated with the
processing of a SCSI command.
150 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: December 2007 Update