Maybe overlaping two concepts, cloning versus imaging. A clone is a duplicate of your existing HD onto another HD. You would swap out the HDs in the event of a failure. An image is a copy of the HD written to a file. In the event of a failure you would use software to write the image onto a new HD ( reinstalling )
Here's a link to some tools to look at,
Five free and reliable cloning tools - TechRepublic, there are others like Acronis true image, easeus todo backup.
Howto article on cloning here,
How to Clone a Hard Drive | PCMag.com
Yes, cloning is what I'm referring to on the Mac. And as I mentioned, the beauty is that you can clone to an external drive, then boot directly from that clone - just hold the "option" key at boot time, and all the boot-able systems will appear, and you choose what you want. Super EZ to test it out after you
think you cloned it. And if you have not tested it, I do not consider it 'cloned'. And if the internal drive crashes, you can be up and running from that clone in minutes, with no fuss/muss. Saved my butt once way back on OS-8 ('Classic'), I think it was. I ran for a week or two, booting from my ZIP drive (remember those?), until I had time to re-install the crashed system on the internal HD.
AFAIK, it takes a 'pro' version in Windows to be able to boot from that clone as an external drive. And if you have to swap drives to test it, well that's a fair amount of trouble.
I know I can clone my Linux system, but AFAIK, it is not easy to boot from that clone w/o some playing around (and/or removing the internal drive). The external clone will have UUIDs that match the internal drive, and that will conflict. I think I once successfully managed to change the UUIDs on the clone, and get all the internal references updated to match, but it was a lot of work and confusing (for me). And things like Remastersys don't seem to handle a full system, with all the installs and config files (which I have on a separate /home partition). I could clone w/o my data, and merge that later, no sweat. But for me, the purpose of the clone is to have all my system changes and updates. Without that, a clean install is probably less trouble.
-ERD50