mtx is a native linux media changer tool, it controls SCSI media changer devices.
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.

In this article, same as others, I'll show you examples of mtx usage, in my case, it's version 1.3.12

Package info

$rpm -ql mtx-1.3.12-501.sl6.x86_64
/usr/sbin/loaderinfo
/usr/sbin/mtx
/usr/sbin/mtx-driveinfo
/usr/sbin/mtx-inventory
/usr/sbin/scsieject
/usr/sbin/scsitape
/usr/sbin/tapeinfo
...

mtx-driveinfo and mtx-inventory are hacked by me for particular purpose, will tell you more in other articles.

SYNOPSIS

mtx [-f <scsi-generic-device>] [nobarcode] [invert] [noattach] command [ command ... ]

The list of the commands of mtx:

Inquiry, Inventory, status, load, unload, transfer, Invert, First, Last, Next, Position, Eject

Here are examples for these commands

Inquiry

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 address).

# mtx -f /dev/changer3 inquiry
Product Type: Medium Changer
Vendor ID: 'IBM     '
Product ID: '03584L32        '
Revision: 'B540'
Attached Changer API: No

Inventory -- not applicable to all libraries

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 from 1.

# mtx -f /dev/changer3 status
  Storage Changer /dev/changer3:1 Drives, 46 Slots ( 16 Import/Export )
Data Transfer Element 0:Full (Storage Element 3 Loaded):VolumeTag = A04592
      Storage Element 1:Full :VolumeTag=A04590
      Storage Element 2:Full :VolumeTag=A04591
      Storage Element 3:Empty:VolumeTag=
      Storage Element 4:Full :VolumeTag=A04593
      Storage Element 5:Full :VolumeTag=A04594
      Storage Element 6:Full :VolumeTag=A04595
      Storage Element 7:Full :VolumeTag=A04596
      Storage Element 8:Full :VolumeTag=A04597
      Storage Element 9:Full :VolumeTag=A04598
      Storage Element 10:Full :VolumeTag=A04599
      Storage Element 11:Empty:VolumeTag=
      Storage Element 12:Empty:VolumeTag=
      Storage Element 13:Empty:VolumeTag=
      Storage Element 14:Empty:VolumeTag=
      Storage Element 15:Empty:VolumeTag=
      Storage Element 16:Empty:VolumeTag=
...

Load

 Load media from slot <slotnum> into drive <drivenum>. Drive 0 is assumed if the drive number is omitted.

 load <slotnum> [ <drivenum> ]
# mtx -f /dev/changer3 load 3 0
Loading media from Storage Element 3 into drive 0...done

Unload

unload [<slotnum>] [ <drivenum> ]
Unloads  media from drive <drivenum> into slot <slotnum>. If <drivenum> is omitted, 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.

# mtx -f /dev/changer3 unload 3 0
Unloading drive 0 into Storage Element 3...done

Transfer

[eepos <operation>] transfer <slotnum> <slotnum>
Transfers  media  from  one  slot to another, assuming that your mechanism is capable 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 <operation> 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 documentation).

# mtx -f /dev/changer3 transfer 10 11
# mtx -f /dev/changer3 status
  Storage Changer /dev/changer3:1 Drives, 46 Slots ( 16 Import/Export )
Data Transfer Element 0:Full (Storage Element 3 Loaded):VolumeTag = A04592
      Storage Element 1:Full :VolumeTag=A04590
      Storage Element 2:Full :VolumeTag=A04591
      Storage Element 3:Empty:VolumeTag=
      Storage Element 4:Full :VolumeTag=A04593
      Storage Element 5:Full :VolumeTag=A04594
      Storage Element 6:Full :VolumeTag=A04595
      Storage Element 7:Full :VolumeTag=A04596
      Storage Element 8:Full :VolumeTag=A04597
      Storage Element 9:Full :VolumeTag=A04598
      Storage Element 10:Empty:VolumeTag=
      Storage Element 11:Full :VolumeTag=A04599
...

Invert

-- I don't even see use case for this option
       [eepos <operation>] [invert] [invert2] exchange <slotnum> <slotnum> [<slotnum>]

Move  medium  from  the  first  slot to the second slot, placing the medium currently in the second slot either back into the first slot or into the optional third slot.

First

first [<drivenum>]
Loads drive <drivenum> from the first slot in the media changer. Unloads the drive if there is already media in it (note: you may  need to eject the tape using your OS’s tape control commands first). 

Note that this command may not be what you want on large tape libraries -- e.g. on Exabyte 220, the first slot is usually a cleaning tape.

If <drivenum> is omitted, defaults to first drive.

# mtx -f /dev/changer3 first
Unloading drive 0 into Storage Element 3...done
Loading media from Storage Element 1 into drive 0...done

Last

last [<drivenum>]
Loads  drive  <drivenum>  from the last slot in the media changer. Unloads the drive if there is already a tape in it.

(Note: you may need to eject the tape using your OS’s tape control commands first).

# mtx -f /dev/changer3 last
Unloading drive 0 into Storage Element 1...done
Loading media from Storage Element 30 into drive 0...Source Element Address 1056 is Empty

Note: there is no tape in the last slot in this case

Next

next [<drivenum>]
Unloads the drive and loads the next tape in sequence. If the drive was empty, loads the first tape into the drive.

# mtx -f /dev/changer3 next
Loading media from Storage Element 1 into drive 0...done

Position

position <slotnum>
Positions the robot at a specific slot. Needed by some changers to move to and open the import/export, or mailbox, slot.

# mtx -f /dev/changer3 position 10

Eject

eject, eject tape from tape drive, no robot movement.

Other tools in the same package

In addition to mtx tool, there are other tools in mtx package

loaderinfo

Usage: loaderinfo -f <generic-device>

# loaderinfo -f /dev/changer3
Product Type: Medium Changer
Vendor ID: 'IBM     '
Product ID: '03584L32        '
Revision: 'B540'
Attached Changer: No
Bar Code Reader: No
EAAP: Yes
Number of Medium Transport Elements: 2
Number of Storage Elements: 30
Number of Import/Export Elements: 16
Number of Data Transfer Elements: 1
Transport Geometry Descriptor Page: Yes
Invertable: No
Device Configuration Page: Yes
Storage: Data Transfer, Import/Export, Storage
SCSI Media Changer (rev 2): No
Transfer Medium Transport: ->Data Transfer, ->Import/Export, ->Storage
Transfer Storage: ->Data Transfer, ->Import/Export, ->Storage
Transfer Import/Export: ->Data Transfer, ->Import/Export, ->Storage
Transfer Data Transfer: ->Data Transfer, ->Import/Export, ->Storage
Exchange Medium Transport: None
Exchange Storage: <>Data Transfer, <>Import/Export, <>Storage
Exchange Import/Export: <>Data Transfer, <>Import/Export, <>Storage
Exchange Data Transfer: <>Data Transfer, <>Import/Export, <>Storage

tapeinfo

# tapeinfo /dev/fcnst18
Usage: tapeinfo -f <generic-device>
[root@t1-ppshead ~]# tapeinfo -f  /dev/fcnst18
Product Type: Tape Drive
Vendor ID: 'IBM     '
Product ID: 'ULT3580-TD5     '
Revision: 'BBNE'
Attached Changer API: No
SerialNumber: '00078A2295'
MinBlock: 1
MaxBlock: 8388608
SCSI ID: 1
SCSI LUN: 0
Ready: yes
BufferedMode: yes
Medium Type: 0x58
Density Code: 0x58
BlockSize: 0
DataCompEnabled: no
DataCompCapable: yes
DataDeCompEnabled: yes
CompType: 0x1
DeCompType: 0x1
BOP: yes
Block Position: 0
Partition 0 Remaining Kbytes: -1
Partition 0 Size in Kbytes: -1
ActivePartition: 0
EarlyWarningSize: 0
NumPartitions: 0
MaxPartitions: 1

scsieject -- unlike mtx, this is to control SCSI tape devices, as well as CD/DVD

The  scsieject  command  controls  SCSI  devices  in  a  platform-independent  manner.  As long as 'mtx' works on the platform, so does 'scsieject'.

Usage:

scsieject [-f <scsi-generic-device>] commands

COMMANDS

load 
     Load  the  medium  into  the  drive.  When this command is issued to a CD/DVD drive and the tray is extended the tray will be retracted if the drive is capable of it.
unload   
    Unload the medium from the drive (also known as eject).  When this command is issued to a CD/DVD drive or a  tape  drive  the media will be ejected if the device supports it.
start    
     Start the device.  Some devices require a start command after a media changer has loaded new media into the device.
stop     
     Stop  the  device.   Some  devices  require  a  stop command prior to unloading the medium from the device when using a media changer.
lock     
     Lock the device.  Locks the device so that the medium cannot be removed manually.
unlock   
     Unlock the device.  Unlocks the device so that the medium can be removed manually.

scsitape

I don't use it, I use mt instead, which control magnetic tape drive operation, not generic-scsi-device.

# scsitape -h
Usage: scsitape -f <generic-device> <command> where <command> is:
 setblk <n> | fsf <n> | bsf <n> | eod | rewind | eject | mark <n> |
  seek <n> | read [<blksize> [<numblocks]] | write [<blocksize>]