Secure a connected hard disk in AirPort Utility on Mac
If your base station supports connecting to a USB hard disk, or if you’re using an AirPort Time Capsule, you can secure access to the disk in one of several ways: by setting up an account and password for each user, by setting a disk password, or by using the base station’s existing password.
Important: If you change the way the disk is secured (from user accounts to the device or disk password) or if you change the name of an account, users may not have access to all the files on the disk.
Open the AirPort Utility app on your Mac, located in the Utilities folder in the Applications folder.
In the graphical overview, select the base station you want to configure, then click Edit. You may need to enter a password for the base station.
Click Disks, select the disk or partition you want to add the account to, then choose “With accounts” from the Secure Shared Disks pop-up menu.
Verify that “Enable file sharing” is selected.
To add a user account, click the Add button below the Accounts list, then do the following in the dialog that appears:
Enter a name in the Account Name field.
Enter a password for the account in both password fields.
Click the File Sharing Access pop-up menu, then choose a type of access control.
Read and write allows the user to read and write to the connected disk or partition.
Read only allows the user to only read data on the connected disk or partition.
Not allowed prevents the user from accessing files on the selected disk or partition.
When you’re done, click Save.
Repeat this process to create additional user accounts.
When you’re done, click Update to save your changes.