External Backup with Time Machine


Today’s Question: I’m about to move my images from my internal hard drive to an external hard drive and am thinking about backup. I now use Time Machine and periodically backup with drag and drop to an external hard drive that I keep offsite. I will continue with the offsite backup but wonder if I can use Time Machine for both my internal and external hard drives.

Tim’s Quick Answer: Yes, you can use Time Machine on a Macintosh to back up external hard drives in addition to internal hard drives. However, my personal preference is to use software that creates a synchronized backup of external hard drives so the backup is a perfect match of the original. I use GoodSync software (http://timgrey.me/greybackup) for this purpose.

More Detail: Time Machine is the backup software built into the Macintosh operating system. I highly recommend using Time Machine to back up the internal drive on your computer even if you are also using other software or online tools to back up that drive. That’s because Time Machine makes it remarkably easy to restore from a backup when you accidentally delete files, have a problem with your computer, or buy a new computer.

You can add external hard drives to your Time Machine backup if you want to include those drives. Note that you’ll need to make sure that the hard drive you’re using for the Time Machine backup has enough storage capacity for all of the drives you intend to include.

By default, Time Machine only backs up internal hard drives. So, if you want to include external hard drives in the backup, you’ll need to remove those drives from the exclude list. To do so first make sure the external hard drives you want to include are connected to the computer. Then click the Apple logo on the menu bar and choose System Preferences. Go to Time Machine and click the Options button, which will cause a dialog to appear showing the exclusion list. For each hard drive on the list that you want to include in the Time Machine backup click the name of the drive and then click the minus button (-) at the bottom-left of the list. Click the Save button to apply the changes. Time Machine will then include the non-excluded external hard drives in the backup.

However, I prefer to have individual synchronized backups for each of my external hard drives. Among other things, this makes it much easier to recover from a hard drive failure, because the folder and file structure on the backup drive will be a perfect match of the original. I use GoodSync software (http://timgrey.me/greybackup) for this synchronized backup.

Note, by the way, that I recommend maintaining at least two Time Machine drives for the internal hard drive backup, as well as two backup drives for each external hard drive being backed up. It is also a good idea to use an online backup for an offsite backup solution, such as the Backblaze service (https://timgrey.me/onlinebackup) that I use.