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mc(7)


NAME

  mc - SCSI medium changer interface


DESCRIPTION

  The medium changer (mc) interface provides a means for applications to
  control the robotic medium changers found in tape and optical libraries or
  jukeboxes.

  The mc driver may be used for any supported Small Computer System Interface
  (SCSI) medium changer devices, and potentially for other SCSI-compliant
  changer devices.  Applications use Unix I/O calls (open, close, ioctl) to
  access changer devices, by means of device special files.  Changer device
  special files are typically created in the /dev/changer directory by the
  dsfmgr utility on system startup.  Refer to the dsfmgr(8) Reference Page
  and System Administration if you need to recreate device special files that
  are deleted accidentally. The rz(7) and tz(7) Reference Pages provide
  information on how device names map to SCSI CAM lun addresses.

  The format of a a medium changer device special file name is:

       /dev/changer/mcN

  where N is an integer representing the instance of the device that is
  assigned by dsfmgr at system startup.

  The driver supports a number of ioctl commands that move media in the
  library or return information about the media.  See the header file
  /usr/sys/include/io/cam/mchanger.h for the ioctl commands and their
  associated structs.

  An application opens the device special file corresponding to the changer
  device, executes appropriate ioctl commands, then closes the device special
  file.	 Typically, changer devices are not shared between applications, but
  this is not due to any limitation on the changer or mc driver, but rather
  to the possibility of confusing which media belong to which application.
  An application on a non-cluster system can assure that only it can use a
  changer by opening that changer's device special file for exclusive access,
  by including the O_EXCL flag in the open call, and leaving the file open
  until the application is completely done using the changer.  However, if
  the changer is on a shared bus in a cluster, it is possible for an
  application on each cluster member to open the device, even if each
  specifies O_EXCL, because that only grants exclusive access on the local
  host.	 In this case it may be useful for the application to use a SCSI
  device reservation to assure exclusive access.  (An ioctl command is
  provided to facilitate reserving a changer.)

  Refer to the Software Product Description for a list of supported devices
  under the heading of SCSI CAM Layered Components. Facilities are provided
  in the operating system to allow the addition of some third-party SCSI-
  compliant medium changers.  Under Digital Unix V4.0 and later, refer to the
  ddr_config(8) and ddr.dbase(4) reference pages for instructions. Under
  Digital Unix V3.x, new devices can be added to /sys/data/cam_data.c. See
  that file for instructions.


FILES

  /dev/changer/mc?
      changer device special file

  /usr/sys/include/io/cam/mchanger.h
      header file for changer ioctl commands


SEE ALSO

  Commands: mcutil(1), mcicap(4), dsfmgr(8), scu(8), uerf(8)

  Interfaces: op(7), tz(7), SCSI(7)

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