Desculpe,
tinha esquecido de falar o mtx-changer trabalha legal, faz load e unload normalmente:
root@dti:/etc# /etc/bacula/scripts/mtx-changer /dev/sg4 load 1 /dev/nst0 0
Loading media from Storage Element 1 into drive 0...done
root@dti:/etc# /etc/bacula/scripts/mtx-changer /dev/sg4 unload 1 /dev/nst0 0
Unloading drive 0 into Storage Element 1...
root@dti:/etc#
Segue o status do mt:
root@dti:/etc# mtx -f /dev/sg4 status
Storage Changer /dev/sg4:2 Drives, 39 Slots ( 3 Import/Export )
Data Transfer Element 0:Empty
Data Transfer Element 1:Empty
Storage Element 1:Full :VolumeTag=A00001L4
Storage Element 2:Full :VolumeTag=A00002L4
Storage Element 3:Full :VolumeTag=A00003L4
Storage Element 4:Full :VolumeTag=A00004L4
Storage Element 5:Full :VolumeTag=A00005L4
Storage Element 6:Full :VolumeTag=A00006L4
Storage Element 7:Full :VolumeTag=A00007L4
Storage Element 8:Full :VolumeTag=A00008L4
Storage Element 9:Full :VolumeTag=A00009L4
Storage Element 10:Full :VolumeTag=A00010L4
Storage Element 11:Empty
Storage Element 12:Empty
Storage Element 13:Empty
Storage Element 14:Empty
Storage Element 15:Empty
Storage Element 16:Empty
Storage Element 17:Empty
Storage Element 18:Empty
Storage Element 19:Empty
Storage Element 20:Empty
Storage Element 21:Empty
Storage Element 22:Empty
Storage Element 23:Empty
Storage Element 24:Empty
Storage Element 25:Empty
Storage Element 26:Empty
Storage Element 27:Empty
Storage Element 28:Empty
Storage Element 29:Empty
Storage Element 30:Empty
Storage Element 31:Empty
Storage Element 32:Empty
Storage Element 33:Empty
Storage Element 34:Empty
Storage Element 35:Empty
Storage Element 36:Empty
Storage Element 37 IMPORT/EXPORT:Empty
Storage Element 38 IMPORT/EXPORT:Empty
Storage Element 39 IMPORT/EXPORT:Empty
root@dti:/etc#
Obrigado Fabio