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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 subsystem 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 system
  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 identified 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 during 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 percentage 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 maximizing the volume of I/O in a busy
  system. See the EXAMPLES section for some typical usage scenarios.

				     Note

       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 internal 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 outstanding 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 outstanding
  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

  /sys/BINARY/emx.mod
    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).

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