Apple firmware (bios) enables a total, bootable system copy and restoration with but a few clicks of the mouse. This is perhaps the most underutilised, little known feature of Apple computers. Interested? Follow these instructions:
1) Attach the USB drive and make certain it shows up.
2) Reboot the computer. The moment you hear the chime, press and hold ALT (newer) or CMD-R (older), depending upon age of your Mac.
3) A simple graphical interface will appear with what should be 3 or more icons. 2 of which will be for your internal drive, 1 or more for the USB.
4) Using the cursor controls, choose the “RECOVERY” partition of your internal drive and hit ENTER or the button at the bottom.
5) Select your language.
6) Select “DISK UTILITY” (see screenshot.png)
7) Select the icon on the left which is your internal drive.
8) Select “RESTORE” from the upper-right of the 3-4 options. This drive should now be in the SOURCE entry.
9) Drag the icon for the USB drive to the DESTINATION entry.
In this step, you can backup to a partition on the backup USB drive and ONLY replace the partition. This is what I do. But that would be ONLY if the backup drive is substantially larger than the internal drive and you don’t want to waste the space.
Else, if the 2 drives are closely matched, then select the primary (not indented) and see what happens. It may reject it. In which case you simply use the indented instead. It will rename that partition anyway, to match the drive it is copied from.
10) Double-check that the SOURCE is your internal drive and that the DESTINATION is the external, USB drive. Else, you will wipe-out your entire computer. Not good.
11) Press RESTORE and accept the warning for total doom.
12) Between 35 minutes and an hour and a half later, your computer will have made a complete, bootable copy.
What’s more, the external USB drive will now have 2 partitions, one which is a bootable copy of your internal drive, and the other a RECOVERY partition. When next you conduct this backup, you will again boot from the internal RECOVERY partition, not that of the external USB drive, just to play it safe (and it is faster).