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[WARNING: This document is of historical value only! Please read
 'mtxl.README.html' and 'man mtx' for current documentation! The only
 thing useful here is examples of how to use the 'tar' command for
 multi-tape backups.
]

		MTX - SCSI Tape Medium Changer Control Program

	Version 1.1 for Linux, Solaris, IRIX, Digital Unix, and OpenVMS

				  2 June 1998

			       Leonard N. Zubkoff
			       Dandelion Digital
			       lnz@dandelion.com

	 Copyright 1997-1998 by Leonard N. Zubkoff <lnz@dandelion.com>


				 INTRODUCTION

The MTX program controls the robotic mechanism in DDS Autoloaders such as the
Seagate 4586NP (Archive Python 28849-XXX).  This program is also reported to
work with the Seagate 4584NP, HP Surestore 12000, Quantum DLT 2500 XT, and AIWA
DL-210.  The 4586NP responds to both Logical Units 0 and 1 on the selected
Target ID.  Logical Unit 0 supports commands from the SCSI-3 Sequential Stream
Device Command Set and must be accessed via the SCSI tape devices /dev/st<N>.
Logical Unit 1 only supports commands from the SCSI-3 Medium Changer Command
Set and must be accessed via the SCSI Generic devices /dev/sg<N>.  In addition,
Logical Unit 0 also acts as an Attached Medium Changer and supports the READ
ELEMENT STATUS and MOVE MEDIUM commands.  Since using the Primary Device
(Logical Unit 0) via the Attached Medium Changer interface is sufficient for
the commands provided by this program, Logical Unit 1 is not normally used.
The AIWA DL-210, by contrast, does not support the Attached Medium Changer
commands on Logical Unit 0 and so MTX must be used with Logical Unit 1 via the
SCSI Generic devices /dev/sg<N>.  Note that when using the SCSI Generic devices
the Linux kernel option "max_scsi_luns=2" may be necessary.

Medium Changers support four types of elements: Medium Transport Elements,
Storage Elements, Import Export Elements, and Data Transfer Elements.  For the
limited case of DDS Autoloaders, only the Data Transfer Element and Storage
Element types are really applicable.  The Data Transfer Element is the primary
device where a volume can be loaded to actually perform data transfers.  A
Storage Element is a place a volume can be when it is waiting to be used.  For
a DDS Autoloader, the Storage Elements are the slots in the cartridge where
tapes may be placed, and the Data Transfer Element is the tape mechanism.

Every Medium Changer Element has a unique integer Element Address that
identifies it in the address space of all Elements known to the Medium Changer.
For the 4586NP, the Data Transfer Element is Address 1 and the Storage Elements
are Addresses 2-5 or 2-13.  To simplify the human interface, this program does
not use Element Addresses directly.  Rather, it uses Storage Element Numbers
which range from 1 to the number of Storage Elements available.

The specific tape device to be operated on can either be supplied on the
command line with the "-f <tape-device>" option, or via the TAPE environment
variable.


				 BUILDING MTX

The Makefile contains sections for Linux, Solaris/SPARC, SGI IRIX, and Digital
UNIX.  Comment/uncomment as necessary for the target environment.  For OpenVMS,
see the file "vms/000readme" for information on building MTX; a VMS release
including pre-built binaries should be available from the WKU VMS FILESERV
ARCHIVES, which are located at URLs http://www2.wku.edu/www/fileserv/ and
ftp://ftp.wku.edu/vms/fileserv/.


				   COMMANDS

MTX provides the following commands:


mtx [ -f <tape-device> ] inquiry

The "inquiry" command reports the Vendor ID, Product ID, and Revision from a
SCSI INQUIRY command.

kelewan:~# setenv TAPE /dev/st0

kelewan:~# mtx inquiry
Vendor ID: 'ARCHIVE ', Product ID: 'Python 28849-XXX', Revision: '4.CM'


mtx [ -f <tape-device> ] status

The "status" command reports on the status of the DDS Autloader.  The report
indicates the status of the Data Transfer Element and each of the Storage
Elements.  In the first example, no tape is currently loaded.  In the second
example, Storage Element Number 1 is loaded.  The Storage Element loaded into
the Data Transfer Element is usually reported by the DDS Autoloader, or it can
be inferred by MTX if there is only a single empty Storage Element.

kelewan:~# mtx status
Data Transfer Element:	Empty
Storage Element 1:	Full
Storage Element 2:	Full
Storage Element 3:	Full
Storage Element 4:	Full


kelewan:~# mtx status
Data Transfer Element:	Full (Storage Element 1 Loaded)
Storage Element 1:	Empty
Storage Element 2:	Full
Storage Element 3:	Full
Storage Element 4:	Full


mtx [ -f <tape-device> ] load <storage-element-number>

The "load" command loads the volume in Storage Element <storage-element-number>
into the Data Transfer Element.  An error is signaled if the Data Transfer
Element is already full.


mtx [ -f <tape-device> ] unload [ <storage-element-number> ]

The "unload" command unloads the volume in the Data Transfer Element into
Storage Element <storage-element-number>.  If <storage-element-number> is not
provided, then the volume is unloaded back into the Storage Element from which
it was originally loaded, if known.  An error is signaled if the Storage
Element is already full.


mtx [ -f <tape-device> ] first

The "first" command unloads any volume in the Data Transfer Element and then
loads the volume in the lowest numbered non-empty Storage Element.  If the
correct Storage Element is already loaded, the unload/load is suppressed.


mtx [ -f <tape-device> ] next

The "next" command unloads any volume in the Data Transfer Element and then
loads the volume in the lowest numbered non-empty Storage Element above the
Storage Element that was just unloaded.  If there is no next Storage Element,
the unload is still performed and the Data Transfer Element will be left empty
so that the volume is not accidentally overwritten.


mtx [ -f <tape-device> ] last

The "last" command unloads any volume in the Data Transfer Element and then
loads the volume in the highest numbered non-empty Storage Element.  If the
correct Storage Element is already loaded, the unload/load is suppressed.


mtx [ -f <tape-device> ] previous

The "previous" command unloads any volume in the Data Transfer Element and then
loads the volume in the highest numbered non-empty Storage Element below the
Storage Element that was just unloaded.  If there is no previous Storage
Element, the unload is still performed and the Data Transfer Element will be
left empty so that the volume is not accidentally overwritten.


The interface is designed to allow both explicit control of precisely which
Storage Element is loaded, as well as sequential access among only the Storage
Elements that actually have volumes present.  Thus for example, one way of
using MTX would be to perform Monday's incremental backups on Storage Element
1, Tuesday's on Storage Element 2, and so on.  Multi-volume full backups are
also conveniently supported, as in:

setenv TAPE "/dev/st0"

mtx status

mtx first

time tar --create --one-file-system --atime-preserve \
	 --listed-incremental `date +%y%m%d`.ss \
	 --multi-volume --new-volume-script "mtx next" \
	 --directory /  <wherever>

mtx first

time tar --compare --multi-volume --new-volume-script "mtx next" \
	 --directory /

mtx unload


			   LINUX KERNEL REQUIREMENTS

Because the MOVE MEDIUM command may require 60 seconds or more to perform a
volume load or unload request, a longer timeout must be provided.  Linux
kernels 2.0.30 and 2.1.28 should already contain a long enough timeout.  For
earlier kernels, edit the file "linux/drivers/scsi/scsi_ioctl.c" and add the
following entries to the switch statement in ioctl_command:

      case MOVE_MEDIUM:
      case READ_ELEMENT_STATUS:
	timeout =  5 * 60 * HZ;	/* 5 minutes */
	retries = 1;
	break;

For older kernels, you may also need to add the following definitions to
"linux/include/scsi/scsi.h":

#define MOVE_MEDIUM           0xa5
#define READ_ELEMENT_STATUS   0xb8

Note also that "/usr/include/scsi" should be a symbolic link to the directory
"linux/include/scsi" from your kernel source.

Finally, when using MTX you may see some console messages from the SCSI tape
driver mentioning that there is no tape present.  These can safely be ignored.