Is this the right way to use dd for a full backup? Sadly my device (sm-g3185) isn't supported by any of the CWM or NANDbackup so I am trying to do a backup manually. I found this thread which tells me to open one terminal (I'm on Arch Linux) and run:

adb forward tcp:5555 tcp:5555
adb shell
su
/system/xbin/busybox nc -l -p 5555 -e /system/xbin/busybox dd if=/dev/block/mmcblk0


And then  another terminal and run:

adb forward tcp:5555 tcp:5555
cd /path/to/store/the/backup
nc 127.0.0.1 5555 | pv -i 0.5 &gt; mmcblk0.raw


I did all this and it seems to be working. However, there was a delay of a few seconds between launching the dd command in terminal1 and the nc command in terminal2. 

Can I trust the backup I created in this way? Doesn't this mean that I've lost some of the output of dd? Shouldn't these be run concurrently or, at least, shouldn't the nc command be started before the dd one?
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.