CH(4)                     OpenBSD Programmer's Manual                    CH(4)

NAME
     ch - scsi media-changer (juke box) driver

SYNOPSIS
     ch? at scsibus? target ? lun ?

DESCRIPTION
     The ch driver provides support for SCSI juke boxes.  It allows many slots
     of media to be multiplexed between a number of drives.

     A SCSI adapter and a logical scsibus must also be separately configured
     into the system before a SCSI changer can be configured.

     As the SCSI adapter is probed during boot, the SCSI bus is scanned for
     devices.  Any devices found which answer as "Changer" type devices will
     be ``attached'' to the ch driver.  The first device found will be at-
     tached as ch0 and the next ch1, etc.  It is also possible to specify what
     ch unit a device should come on-line as; refer to scsi(4) for details on
     kernel configuration.

KERNEL CONFIGURATION
     In configuring, if an optional count is given in the specification, that
     number of SCSI media changers are configured.  Most storage for them is
     allocated only when found so a large number of configured devices is
     cheap (once the first has included the driver).

IOCTLS
     The following ioctl(2) call applies to the changer.  It is defined in the
     header file <sys/chio.h>.

     CHIOOP      This appears to be a ``do-everything'' call.

FILES
     /dev/ch[0-9]  device entries

SEE ALSO
     cd(4), scsi(4), sd(4), st(4)

DISCLAIMER
     These manpages were derived from the FreeBSD documentation of the generic
     SCSI drivers.  Since naming and calling conventions may have diverged or
     suffered port specific changes, please review the appropriate header
     files and configuration file for your port.

HISTORY
     The ch driver appeared in 386BSD 0.1.

OpenBSD 2.9                     March 28, 1997                               1
