External hard drives are a wonderful way to offload data from the Mac’s mostly sparse internal hard drive. Since external hard drives are not expensive – 2 terabytes cost well under 100 Euros – they are still the cheapest way to store data on the Mac. However, external hard disks can be lost quickly and should therefore be encrypted as a matter of principle in order to hide the data from the eyes of third parties. On the Mac, this is easily done with the Hard Disk Utility.
How to Encrypt Hard Drive on Mac Using Disk Utility
Step 1: If it is not a blank or new hard drive, you must first copy all data to more external hard drives. This is important because the hard drive must be formatted for encryption and all data will be deleted.
Step 2: After that, open the Disk Utility app. The easiest way to do this is to use the Spotlight search (small magnifying glass in the upper right corner).
Step 3: Select "View"> "Show all devices" in the menu bar at the top.
Step 4: On the left, click the hard drive you want to encrypt.
Step 5: Then click "Delete" at the top.
Step 6: Select "GUID Partition Table" as the scheme and "Mac OS Extended (journaled, encrypted)" as the format.
Step 7: A window pops up where you can assign a password. Then click on "Select" and then on "Erase" to reformat the disk with the encryption. This may take a while.
Step 8: After that, click "Done" and close the disk utility.
Step 9: The hard disk will now be mounted.
Step 10: The next time you mount it, macOS will ask for the password you assigned in step 7. You can save this on your Mac in Keychain so you don’t have to do this again.
Step 11: Copy the data back to the now-encrypted external hard drive and delete it from the other disk.
How to Encrypt Hard Drive on Mac Using File Vault
By the way: If you use FileVault, it is even easier. But you have to encrypt your system hard disk on the Mac, which can lead to problems in case of a defect. So you should make sure to always create a Time Machine backup. We will explain how to make a backup on your Mac here.
For FileVault encryption, open System Preferences, select "Security" and enable FileVault. For security, select to allow your iCloud account to unlock the hard drive.
The Mac will now encrypt all data on the internal disk after a reboot. Afterwards, you can additionally encrypt external disks simply in the Finder by right-clicking and selecting "Encrypt this disk".
With FileVault, the Mac is completely encrypted.