How to back up my mac
how do I back up my mac before I install new os?
iMac 27″, macOS 10.12
Do you have a Rescue Plan In-Place. This comprises having 3 Backups using 2 methods and 1 Off Site incase of Theft, Loss or Natural Disasters. A Time Machine Backup is very useful and can be used to Revert to Previous Working macOS. For addition purposes - two Tested Bootable Clones each to separate external drives. This is insurance incase the upgrades goes sideways. At least one Tested Clone and / or Time Machine Backup should be Off - Site
The above may appear as over-kill but should the computer content be that important it would be well worthwhile doing so.