dd_bak.sh

#!/bin/bash

# restore with the following command:
# gunzip --stdout <filename>.img.gz | dd bs=10M of=/dev/sdX

# pv(1) is optional and provides a progress bar
# just remove it from the pipe, when you don't want it

DATE=$(date +"%Y-%m-%d_%H-%M")
GREEN='\033[1;32m'
RED='\033[1;31m'
NC='\033[0m'

if [[ "$1" == "-h" || "$1" == "--help" || "$1" == "" ]]; then
	echo -e "simple dd backup tool by c5e3"
	echo -e "must be run as root!"
	echo -e "usage:"
	echo -e "\tdd_bak.sh <sdX> <destination folder>"
	exit 1
else
	if [[ $EUID -ne 0 ]]; then
		echo "try again as root" 1>&2
		exit 1
	fi
	echo -ne "make backup from ${GREEN}/dev/$1${NC} to ${RED}$2${HOSTNAME}_$1_$DATE.img.gz${NC}? [y/n] "
	read confirm

	if [[ "$confirm" == "y" ]]; then
		dd bs=10M if=/dev/$1 | pv | gzip > $2${HOSTNAME}_$DATE.img.gz
	else
		echo -e "${RED}no backup created!${NC}"
		exit 1
	fi
fi

I have just discovered that pigz has --rsyncable built-in (from upstream, without a patch) and other similar switches such as --independent. In addition since pigz compresses using threads to make use of multiple processors and cores, you will most likely get far better performance. Finally pigz was written by Mark Adler (a co-author of the zlib compression library and gzip) so I would be fairly confident in its reliability.

So if you are planning to continue with a gzipped image or archive, pigz with appropriate switch(es), might be a better option.