CH(4)

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

SYNOPSIS
device ch
device ch1 target 4 lun 0

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

A scsi adapter 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. In FreeBSD releases prior to 2.1, the first found will be attached as ch0 and the next, ch1 etc. Beginning in 2.1 it is 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 in the header file sys/chio.h.
CHIOOP This appears to be a 'do-everything' call.

NOTES
The ch driver was added to the system by Stefan Grefen (grefen@goofy.zdv.uni-mainz.de) who apparently had such a device however It appears as though no-one I have heard of has ever used this driver. If you use it please let me know so I can test changes. Stefan appears to have suffered net.death (or at least net.disconnection). I (julian) have never used this device. If you do please re-write this man page and send it to me..

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

DIAGNOSTICS
None.

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

HISTORY
The ch driver appeared in 386BSD 0.1.