Disk Cloning

Carbon Copy Cloner

A bootable backup of your current OS will save you countless hours if the upgrade goes awry.

http://www.bombich.com/

SuperDuper is the wildly acclaimed program that makes recovery painless, because it makes creating a fully bootable backup painless

http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html

A pretty comprehensive piece on the best backup for Mac.

https://www.cloudwards.net/best-mac-backup/