Tech Tip for Mac Users, How to Add a Mac Formatted External Drive to Time Machine

If you read my previous post regarding moving your Photos Library to an external drive and saw that I have Time Machine configured to back up my external drive, you may be wondering how to do this yourself. Please note, these instructions assume you have either a Mac OS Extended (Journaled) or APFS volume, other types may not work. Additionally, you cannot back up data stored on a Time Machine volume using this method. I've been backing up my large external drive using this method for over five years.

1. Connect your external drive
2. Open the Time Machine Preferences.
3. Click on the "Options" Button
4. Locate your external drive on the list of excluded items.
5. Select your external drive and click the minus sign and then click the "Save" button
6. Start a backup manually. This will take some time as it will do the standard incremental backup of everything else normally backed up, but will perform full backup of the new drive you added.

Time Machine will back up your external drive any time the external drive is connected and mounted during a Time Machine backup. Time Machine will not provide any error and will simply skip backing up the external drive if it is not available. You can also backup multiple external drives using this method.