I've seen this question on how to backup an SD-card. It's the same solution I would come up with myself; that is basically:
dd if=/dev/blabla of=/home/user/some_file.img`
But my question is if using the argument
bs=1M makes any difference. It does when I'm writing to the card, so I suppose it does when I'm reading from it. Is my assumption correct? In the question I referred to earlier, it differs in different answers.