.\"	$OpenBSD: ch.4,v 1.11 2007/05/31 19:19:49 jmc Exp $
.\"
.\" Copyright (c) 1996
.\"	Julian Elischer <julian@freebsd.org>.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
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.Dd $Mdocdate: May 31 2007 $
.Dt CH 4
.Os
.Sh NAME
.Nm ch
.Nd scsi media-changer (juke box) driver
.Sh SYNOPSIS
.Cd "ch? at scsibus?"
.Sh DESCRIPTION
The
.Nm
driver provides support for SCSI juke boxes.
It allows many slots of media to be multiplexed between a number of drives.
.Pp
A SCSI adapter and a logical scsibus must also be separately configured
into the system before a SCSI changer can be configured.
.Pp
As the SCSI adapter is probed during boot, the SCSI bus is scanned for devices.
Any devices found which answer as
.Qq Changer
type devices will be
.Dq attached
to the
.Nm
driver.
The first device found will be attached as
.Em ch0
and the next
.Em ch1 ,
etc.
It is also possible to specify what
.Nm
unit a device should come on-line as; refer to
.Xr scsi 4
for details on kernel configuration.
.\" .Sh IOCTLS
.\" The following
.\" .Xr ioctl 2
.\" call applies to the changer.
.\" It is defined in the header file
.\" .Aq Pa sys/chio.h .
.\" .Bl -tag -width DIOCSDINFO
.\" .It Dv CHIOOP
.\" This appears to be a
.\" .Dq do-everything
.\" call.
.\" .El
.Sh FILES
.Bl -tag -width /dev/ch[0-9] -compact
.It Pa /dev/ch[0-9]
device entries
.El
.Sh SEE ALSO
.Xr chio 1 ,
.Xr cd 4 ,
.Xr intro 4 ,
.Xr scsi 4 ,
.Xr sd 4 ,
.Xr st 4
.Sh HISTORY
The
.Nm
driver appeared in 386BSD 0.1.