mtx - control SCSI media changer devices
mtx [-f <scsi-generic-device>] [nobarcode] [invert] [noattach] command [ command ... ]
The mtx command controls single or multi-drive SCSI media changers such as tape changers,
autoloaders, tape libraries, or optical media jukeboxes. It can also be used with media
changers that use the 'ATTACHED' API, presuming that they properly report the MChanger bit
as required by the SCSI T-10 SMC specification.
The first argument, given following -f , is the SCSI generic device corresponding to your
media changer. Consult your operating system's documentation for more information (for
example, under Linux these are generally /dev/sg0 through /dev/sg15, under FreeBSD these
are /dev/pass0 through /dev/passX, under SunOS it may be a file under /dev/rdsk).
The 'invert' option will invert (flip) the media (for optical jukeboxes that allow such)
before inserting it into the drive or returning it to the storage slot.
The 'noattach' option forces the regular media changer API even if the media changer
incorrectly reported that it uses the 'ATTACHED' API.
The 'nobarcode' option forces the loader to not request barcodes even if the loader is
capable of reporting them.
Following these options there may follow one or more robotics control commands. Note that
the 'invert' and 'noattach' options apply to ALL of robotics control commands.
--version Report the mtx version number (e.g. mtx 1.2.8) and exit.
inquiry Report the product type (Medium Changer, Tape Drive, etc.), Vendor ID, Product
ID, Revision, and whether this uses the Attached Changer API (some tape drives
use this rather than reporting a Medium Changer on a separate LUN or SCSI
noattach Make further commands use the regular media changer API rather than the
_ATTACHED API, no matter what the "Attached" bit said in the Inquiry info.
Needed with some brain-dead changers that report Attached bit but don't respond
to _ATTACHED API.
inventory Makes the robot arm go and check what elements are in the slots. This is needed
for a few libraries like the Breece Hill ones that do not automatically check
the tape inventory at system startup.
status Reports how many drives and storage elements are contained in the device. For
each drive, reports whether it has media loaded in it, and if so, from which
storage slot the media originated. For each storage slot, reports whether it is
empty or full, and if the media changer has a bar code, MIC reader, or some
other way of uniquely identifying media without loading it into a drive, this
reports the volume tag and/or alternate volume tag for each piece of media. For
historical reasons drives are numbered from 0 and storage slots are numbered
load <slotnum> [ <drivenum> ]
Load media from slot <slotnum> into drive <drivenum>. Drive 0 is assumed if the
drive number is omitted.
unload [<slotnum>] [ <drivenum> ]
Unloads media from drive <drivenum> into slot <slotnum>. If <drivenum> is omit-
ted, defaults to drive 0 (as do all commands). If <slotnum> is omitted,
defaults to the slot that the drive was loaded from. Note that there's currently
no way to say 'unload drive 1's media to the slot it came from', other than to
explicitly use that slot number as the destination.
[eepos <operation>] transfer <slotnum> <slotnum>
Transfers media from one slot to another, assuming that your mechanism is capa-
ble of doing so. Usually used to move media to/from an import/export port.
'eepos' is used to extend/retract the import/export tray on certain mid-range to
high end tape libraries (if, e.g., the tray was slot 32, you might say say
'eepos 1 transfer 32 32' to extend the tray). Valid values for eepos <opera-
tion> are 0 (do nothing to the import/export tray), 1, and 2 (what 1 and 2 do
varies depending upon the library, consult your library's SCSI-level documenta-
Loads drive <drivenum> from the first slot in the media changer. Unloads the
drive if there is already media in it. Note that this command may not be what
you want on large tape libraries -- e.g. on Exabyte 220, the first slot is usu-
ally a cleaning tape. If <drivenum> is omitted, defaults to first drive.
Loads drive <drivenum> from the last slot in the media changer. Unloads the
drive if there is already a tape in it.
Unloads the drive and loads the next tape in sequence. If the drive was empty,
loads the first tape into the drive.
The original 'mtx' program was written by Leonard Zubkoff and extensively revised for
large multi-drive libraries with bar code readers by Eric Lee Green <firstname.lastname@example.org>, to
whom all problems should be reported for this revision. See 'mtx.c' for other contribu-
BUGS AND LIMITATIONS
You may need to do a 'mt offline' on the tape drive to eject the tape before you can issue
the 'mtx unload' command. The Exabyte EZ-17 and 220 in particular will happily sit there
snapping the robot arm's claws around thin air trying to grab a tape that's not there.
For some Linux distributions, you may need to re-compile the kernel to scan SCSI LUN's in
order to detect the media changer. Check /proc/scsi/scsi to see what's going on.
If you try to unload a tape to its 'source' slot, and said slot is full, it will instead
put the tape into the first empty slot. Unfortunately the list of empty slots is not
updated between commands on the command line, so if you try to unload another drive to a
full 'source' slot during the same invocation of 'mtx', it will try to unload to the same
(no longer empty) slot and will urp with a SCSI error.
This program reads the Mode Sense Element Address Assignment Page (SCSI) and requests data
on all available elements. For larger libraries (more than a couple dozen elements) this
sets a big Allocation_Size in the SCSI command block for the REQUEST_ELEMENT_STATUS com-
mand in order to be able to read the entire result of a big tape library. Some operating
systems may not be able to handle this. Versions of Linux earlier than 2.2.6, in particu-
lar, may fail this request due to inability to find contiguous pages of memory for the
SCSI transfer (later versions of Linux 'sg' device do scatter-gather so that this should
no longer be a problem).
The eepos command remains in effect for all further commands on a command line. Thus you
might want to follow eepos 1 transfer 32 32 with eepos 0 as the next command (which clears
the eepos bits).
Need a better name for 'eepos' command! ('eepos' is the name of the bit field in the
actual low-level SCSI command, and has nothing to do with what it does).
This program has only been tested on Linux with a limited number of tape loaders (a dual-
drive Exabyte 220 tape library, with bar-code reader and 21 slots, an Exabyte EZ-17 7-slot
autoloader, and a Seagate DDS-4 autochanger with 6 slots). It may not work on other oper-
ating systems with larger libraries, due to the big SCSI request size. Report problems to
Eric Lee Green <email@example.com>.
Under Linux, cat /proc/scsi/scsi will tell you what SCSI devices you have. You can then
refer to them as /dev/sga, /dev/sgb, etc. by the order they are reported.
Under FreeBSD, camcontrol devlist will tell you what SCSI devices you have, along with
which pass device controls them.
Under Solaris, set up your 'sgen' driver so that it'll look for tape changers (see /ker-
nel/drv/sgen.conf and the sgen man page), type touch /reconfigure then reboot. You can
find your changer in /devices by typing /usr/sbin/devfsadm -C to clean out no-longer-
extant entries in your /devices directory, then find /devices -name hanger -print to find
the device name. Set the symbolic link /dev/changer to point to that device name (if it is
not doing so already).
With BRU, set your mount and unmount commands as described on the EST web site at
http://www.estinc.com to move to the next tape when backing up or restoring. With GNU tar,
see mtx.doc for an example of how to use tar and mtx to make multi-tape backups.
This version of mtx is currently being maintained by Eric Lee Green <firstname.lastname@example.org> for-
merly of Enhanced Software Technologies Inc. The 'mtx' home page is http://mtx.source-
forge.net and the actual code is currently available there and via CVS from http://source-