Prepare your Mac Ho w to
Make a backup
Instead of Time Machine, we’ll use a different tool to save time if you want to roll back, yet still test your full setup with High Sierra. Connect a spare drive and erase it (not just its partition) with a GUID scheme in Disk Utility.
Prepare for cloning
Download SuperDuper ( shirt
pocket.com) to clone your startup disk to the second drive. Set the app’s Copy pop-up menu to your startup disk, its “to” pop-up to your external drive, and “using” to “Backup – all files.”
Click Options. Set “During copy” to “Erase <volume>, then copy files…” and then Click OK > Copy Now > Copy. Once cloning’s done, rename the copy “High Sierra,” make it your startup disk in System Prefs, and restart your Mac.