everything OK with a 2Gb pendrive.
do NOT use a 128Mb because it's not enough: almost 170Mb needed only for install ffmpeg exteplayer3 gstreamer1.0-libav and a867 driver :o)
Code:
dm800 login: root
root@dm800:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root                 1.8G    169.6M      1.7G   9% /
tmpfs                    64.0K         0     64.0K   0% /media
/dev/sda1                 1.8G    169.6M      1.7G   9% /media/usb
tmpfs                    71.0M      5.1M     65.9M   7% /var/volatile
/dev/mtdblock2            3.8M      2.4M      1.3M  64% /boot

good job toysoft
thanks a lot.