emx(7)							 Miscellaneous Information Manual						    emx(7)

NAME

       emx - Device Driver for the Emulex Fibre Channel Host Adapter

SYNOPSIS

       bus emx0 at pci? controller scsiX at emx0
       bus emx1 at pci? controller scsiY at emx1
	.
	.
	.
       bus emxN at pci? controller scsiZ at emxN

DESCRIPTION

       The emx driver controls and manages the Emulex Fibre Channel Host Adapter. The emx driver is fully integrated with the CAM SCSI I/O subsys-
       tem to provide connectivity to FCP (Fibre Channel Protocol, such as SCSI) devices attached via the Fibre Channel adapter.  In  addition	to
       acting as an FCP initiator, the emx driver also functions as a FCP target. CAM target mode peripheral drivers are also supported.

       The emx driver currently provides Class 3 operation in a Switch-based Fabric configuration.

   Tuning the EMX Driver
       Some  Fibre Channel configurations become busy dealing with QUEUE FULL responses that are generated by busy devices.  When this occurs, not
       enough IO requests are completed successfully and the host CPU can fail the busy devices.

       If such problems occur, you can tune the performance of the emx driver by manipulating the values of  the  following  kernel  configuration
       attributes,  which  are	part  of  the I/O subsystem: NPort_Max_IOs (default value 256) NPort_Min_IOs (default value 20) NPort_IORamp_Delay
       (default value 1) NPort_IORamp_Percent (default value 10)

       Configure these attributes at run time, without rebooting the system by using the command /sbin/sysconfig -r command. If  you  want  custom
       settings to persist across a reboot, ensure that the values are written in the system configuration file. To write the values into the sys-
       tem configuration file, create a stanza file and use the /sbin/sysconfigdb command.

       These system configuration attributes enable you to limit I/O via an N_Port.  An N_Port is a hardware entity attached to the end of a Fibre
       Channel	link.  It manages the transmission and reception of Fibre Channel I/O in the form of primitives and frames. Each N_Port is identi-
       fied by a 64-bit worldwide name (WWN) known as the port name.  In a Point-to-Point topology, an N_Port connects to  another  N_Port  via  a
       link. In a fabric topology, the N_Port connects to an F_Port via a link.

       The attributes enable an I/O limiting feature, allowing you to tune IO when devices become too busy to cope with the I/O rate.  When I/O is
       limited to the correct rate, the emx driver allows only the value of NPort_Max_IOs commands to be outstanding to an N_Port at one time dur-
       ing  normal  use.   If  the  device becomes too busy to accept commands the host responds with a QUEUE FULL status message.  The QUEUE FULL
       response triggers an internal temporary maximum I/O limit. This limit is equal to the volume  of  commands  presently  outstanding  to  the
       N_Port to which the device is attached.

       The  internal temporary maximum I/O limit is never less than the value that you specify for NPort_Min_IOs.  The limit increases by the per-
       centage value specified for NPort_IORamp_Percent.  This percentage increase repeats for the time value (in seconds) that  you  specify  for
       NPort_IORamp_Delay.   The  process  continues until the internal temporary maximum I/O limit is equivalent to the value of NPort_Max_IOs or
       when another QUEUE FULL response is received from the device. This logic limits the volume of commands sent to a busy device while maximiz-
       ing  the  volume  of  I/O  in a busy system. See the EXAMPLES section for some typical usage scenarios.	Do not attempt to set the value of
       NPort_Max_IOs to less than the value of NPort_Min_IOs.

RESTRICTIONS

       Due to the way sense data is handled in FCP, CAM SCSI I/O CCB's that have AUTOSENSE disabled (CAM_DIS_AUTOSENSE) will be  rejected  with  a
       CAM_PROVIDE_FAIL status.

       Direct connections without an intervening switch or hub are not supported.

       Due  to	the SCSI-2 limitations inherent in the design of target mode operation in the CAM specification, specifically in the area of sense
       data handling, tagged command queuing is not supported in the target mode portion of the emx driver.

EXAMPLES

       To turn off I/O limiting, use the following run-time configuration command: # /sbin/sysconfig -r io NPort_Max_IOs = 0xFFFFFFFF

       Using the default values of the attributes, assume the emx driver has 30 commands outstanding to an N_Port. When the driver tries  to  send
       another command, the command is rejected with QUEUE FULL status from the device.  This event triggers the emx driver to decrease the inter-
       nal I/O limit from NPort_Max_IOs to a value of 30. The decreased limit prevents the emx driver from sending new commands until an outstand-
       ing  command completes successfully.  The emx driver continues to send and receive commands with only 30 commands outstanding to the N_Port
       at one time.  This status continues until the time value of NPort_IORamp_Delay (by default, one second) has elapsed.   At  this	point  the
       internal  I/O  limit increases by the absolute value calculated from the following equation: (NPort_Max_IOs * NPort_IORamp_Percent)/100 For
       example: (256 * 10)/100 = 25 The value of the internal I/O limit then becomes 30 + 25 = 55.  In	this  scenario,  the  internal	I/O  limit
       increases  every  one  second,  which  is the current time value set for the NPort_IORamp_Delay attribute.  The procedure repeats until the
       internal I/O limit is equivalent to 256, the current value of NPort_Max_IOs.

       Now, assume that the emx driver has only five commands outstanding to an N_Port and it receives a QUEUE FULL response from one of the  out-
       standing  I/Os.	 The emx driver automatically decreases its internal I/O limit from the value of NPort_Max_IOs to be equivalent to 20, the
       current value of NPort_Min_IOs.	This decrease occurs because the emx driver cannot limit the outstanding I/Os to  less	than  the  current
       value of NPort_Min_IOs.

FILES

       The device driver module.

RELATED INFORMATION

       SCSI(7), rz(7).

   See Also
       System Administration

       emxmgr(8), sys_attrs_io(5), sysconfig(8), and sysconfigdb(8).  delim off

																	    emx(7)