Is this the right way to use dd for a full backup?
I let it run and after it finished, dd reported:

7818182656 bytes (7.3GB) copied, 1245.237601 seconds, 6.0MB/s


And ls -l mmcblk0.raw on my computer shows:

-rw-r--r-- 1 terdon terdon 7818182656 Nov 10 14:45 mmcblk0.raw


Since the file is the right size, presumably the backup was successful.