Best Practise: How to safely test OS X Yosemite before using it for production

*** Update: As this is a reoccurring topic, I updated this: Originally written for Mavericks (OS X 10.9) in 2013, I updted this for Yosemite (OS X 10.10). The topic hasn’t changed from 2013 when Apple released a free update to OS X via the App Store.
If you update your production machine to a new version of OS X without an update and without having it tested thoroughly beforehand, then the chance is high that you’ll run into serious issues. Regardless which software you use for production! ***

In the light of the latest OS X upgrade I have been asked how to safely test a new version of OS X and be able to revert in case there are problems.

Best Practice to test a single Mac with a new version of OS X

The idea is to test in real-life all applications tools and devices needed for production, so that when an important application isn’t compatible or a printer doesn’t work, you can safely revert back to your last working state (and downgrade to the previous version of OS X: Mountain Lion). Of course you could first Google it and trust the experience of others, however a hands-on test often shows a different picture than others might have painted and it gives you the certainty that it will work for you.

I am sure there are many ways, but here’s mine that I have used successfully for many years:

  1. Buy an external hard disk that is at least as large as your internal hard disk (“Macintosh HD”) and connect it to your Mac.
  2. Use Disk Utility to format the external disk as “Mac OS Extended (Journaled)” and in options “GUID Partition Table”.
  3. Download Carbon Copy Cloner ( It has a free trial for 30 days, however I strongly recommend purchasing it (I have no shares in that company ;-) as it can save you a lot of trouble and money.
    And Murphy says “The only backup you’ll ever need is the one that you didn’t make.”
  4. Clone your hard disk to the external disk. So source is “Macintosh HD” and target is “External Drive”. Clone it completely. Everything. Bootable. Note that CCC tells you what it will create before doing it. Read the manual if you are unsure.
  5. Important: Reboot your Mac and hold the Option key pressed. Boot from the external hard disk. Note: This might take  longer than normal, as you are using a connection that is typically a bit slower than an internal hard disk. Test whether everything works as before (ignore the slight difference in speed), it’s important to check that this is a real clone. If everything has worked fine, that’s your 1:1 backup and it’s even bootable.
  6. Shut down your Mac. Unplug external hard disk. Restart.
  7. Now upgrade your Mac to the new OS X (e.g. Mavericks or Yosemite).
  8. Look for upgrades of the applications and tools you use, update your printer drivers etc.
  9. Important: Test everything thoroughly. Test all the applications you use frequently, all goodies, see whether you like the UI, whether all your input and output devices work (scanners, printers etc.). You can even simulate production.
  10. If everything works fine, you are done and can enjoy the new OS X. Ignore the rest of this list ;-)

If something doesn’t work correctly or you can’t produce anymore and you want to go back to your previous OS X that was working fine, here’s how:

  1. First make sure that you save everything important that you have created using the new OS X, e.g. if you created a QuarkXPress document under Mavericks already and you’ll still need that after reverting, save it to a USB stick (or something similar).
  2. Now shutdown your Mac. Connect the external hard disk again.
  3. Important: Start your Mac from the external hard disk (by holding the Option key and choosing the external drive).
  4. Use CCC (Carbon Copy Cloner) to duplicate the cloned drive back to your internal hard disk. Clone everything back from source “External Drive” to target “Macintosh HD”. That’s important, don’t clone it the other way around.
  5. Shut down your Mac. Remove external hard disk.
  6. Restart your Mac. Everything should be now exactly the same as it was before you upgraded OS X. Test it to be sure.
  7. Remember to copy any files you saved on the USB stick to your drive and continue working. Make a mental note to try that in a few weeks again once the applications that haven’t worked correctly are updated to support Mavericks.

Let me know please if this worked for you.