Choose a backup disk and set encryption options on Mac
Turn on Time Machine, add a backup disk or change to a different one, or adjust other settings.
Note: You may want to set up Time Machine in the evening so that the initial backup can be done overnight. If you back up to a Time Capsule or AirPort Extreme (802.11ac), the initial backup may be faster if your Mac is in the same room as the Time Capsule or AirPort Extreme (802.11ac), or if you connect your Mac to one of the Ethernet ports on the Time Capsule or AirPort Extreme (802.11ac). Subsequent backups take less time.
On your Mac, choose Apple menu > System Settings > General, then click Time Machine .
Click Add Backup Disk or click the Add button .
The option you see depends on whether you have one or more backup disks already set up.
Choose a disk or backup location from the list.
Time Machine can’t back up to a disk formatted for Windows. If you connect a disk formatted for Windows, it can be reformatted (permanently removing all data) to a Mac filesystem format and used as a backup disk.
Click Set Up Disk.
If a new window appears, you can select the maximum space used for backups and choose whether to encrypt backups. Click Done after selecting settings.
If you’re asked to erase the disk, click Erase or select a different volume.
Important: Erasing permanently removes all files on the disk, so do it only if you no longer need the files or have copied them to a different disk.
If you chose to encrypt backups (in step 5), type a password for the backup disk.
You may need to provide the password when you connect the disk to your Mac, or when you disconnect the disk or restart your Mac.
If you previously used a Time Capsule or networked disk for unencrypted backups and want to turn on encryption now, Time Machine must first erase the unencrypted backup before starting an encrypted backup.
To use multiple backup disks, repeat these steps for each disk.
If you keep files on your backup disk, Time Machine won’t back up those files, and the space available for Time Machine backups is reduced. See Types of disks you can use with Time Machine.