If you’re working on a Linux image for your single board computer (e.g. Raspberry Pi, OlinuXino, BeagleBone Black, etc.) and you notice that the compression of gzip sucks for the backup image, you need to re-format the SD card. For example, I created a Debian image on a card, which was partitioned for the whole 4GB. Now, we know that only the first few megabytes will be used, and the rest will be empty. However, if you’ve previously used the card (or you might see this with a factory-fresh card), the rest of the card will not be zeros. This will result in a poor compression ratio. My 4GB compressed to 3.1GB. Not great.
How To Backup an SD Card Image
Backing up an image for the Raspberry Pi, BeagleBone Black, OLinuXino, etc.
Let’s say you’re trying to build Linux for your single board computer, and you need to back up the operating system (which, more than likely, is on an SD card). With a relatively small SD card (say, 4GB), you can copy the whole card, zip it, and be able to store/share the image file. It also makes restoring pretty simple.