[dnanian]

What's "Mirror Image", Catnap?

To boot back to the main drive, just use the Startup Disk preference pane in System Preferences.

Do remember, too, that a "Safety Clone" creates a sandbox, not a backup. It's more of a checkpoint of your system files, and doesn't back up any of your personal stuff. You'd also likely want to place it on its own partition, alongside a real backup. That partition need only be about 8-12GB, depending on your particular install.