Nandroid backup stuck at last few files

I've been backing up my device (128GB internal storage) fully through: adb exec-out "dd if=/dev/block/mmcblk0 2>/dev/null" > H:\mmcblk0.img (I specifically need a full system image this way, that's why I'm doing it) As you know, adb has no progress bar. Right now, the file on my PC mmcblk0.img seems to be stuck at 125GB and has been for about 25 minutes or so, and I'm not sure what this means. The properties tab also shows the last modified date as about an hour ago, which is pretty strange. (mmcblk0.img = 125136398.233 kilobytes) When I run cat/proc/partitions, mmcblk0 on my phone is 122142720 kilobytes My napkin math says the PC image is about 3GB larger, but I haven't yet disconnected the cable since I'm afraid if I don't let the image complete till the end, it could end up as unreadable due to missing important information from the partition structure. However, if the last modified date is accurate, it might mean it spent an hour basically doing nothing. Does anybody have an idea of what I should do in this case? Is the image file useless or corrupt then if I unplug my cable? I'd rather not restart the whole thing again, as backing up 128GB of data takes an insane amount of time. If there's a way to somehow view or mount the image to check for that, it would be really amazing. Maybe like a Windows tool, or if not Linux even. I just want to view it basically and check that everything is fine.