ejection is different than unmounting
you can do the same flashing by running an OS from the SD, in this case the eMMC is /dev/mmcblk2 and it is already unmounted, you don't need jumdrive and the PC, it is always useful to have a spare OS on an SD
you can do the same flashing by running an OS from the SD, in this case the eMMC is /dev/mmcblk2 and it is already unmounted, you don't need jumdrive and the PC, it is always useful to have a spare OS on an SD