Warning: When you encrypt a hard drive, if you forget or misplace your password, you will be unable to access your data. HGST is not responsible for data lost in this process and is unable to provide any form of data recovery if needed.
Connect your external drive to your Mac.
Open Finder and right-click on the drive.
Select the Encrypt option as shown in the screenshot below:
Set your password, and enter a second time to verify it. Also provide a hint to help in case you forget the password. It is suggested that you write down your password and put it in a safe place just in case.
Click “Encrypt Disk” to begin the encryption process:
Encrypting the drive is a slow process and will take on average 1 Minute per GB.
After the drive has been encrypted, you will be required to enter your chosen password to access the data: