I find myself working with Raspbian disk images fairly often. A typical workflow is:

• Download the disk image.
• Mount the filesystem somewhere to check something.
• Make some changes or install packages just to check something else.
• Crap I’ve made changes.

…at which point I need to fetch a new copy of the image next time I want to start fresh.

Sure, I could just make a copy of the image and work from there, but what fun is that? This seemed like a perfect opportunity to learn more about the device mapper and in particular how the snapshot target works.