OS X Mountain Lion: Choose a backup disk and set encryption options

This article has been archived and is no longer updated by Apple.
Choose a Time Machine backup disk and set encryption options

Follow these instructions to turn Time Machine on, add a backup disk or change to a different one, or adjust other settings.

Note: The first backup may take a while. You may want to set up Time Machine in the evening so that the initial backup can be done overnight. If your backup disk is a Time Capsule, the initial backup may be faster if you leave your computer in the same room as the Time Capsule, or use an Ethernet cable to connect your computer to one of the Ethernet ports on the Time Capsule. Subsequent backups take less time because only items that have changed are backed up.
  1. Choose Apple menu > System Preferences, and then click Time Machine.
  2. Slide the switch to On if Time Machine is off.
  3. Click the Select Disk button if it’s available. Otherwise, if you already have multiple backup disks, click “Add or Remove Backup Disk” at the bottom of the list of disks.
  4. Choose a disk where backups will be stored. If you’ve already set up one or more backup disks, choose from the list of “Other Available Disks.”

    Every available disk that can be used to store backups is listed. If you partitioned a disk, the partitions are listed.

    Time Machine can’t back up to an external disk connected to an AirPort Extreme, or to an iPod or disk formatted for Windows.

  5. Click “Use Disk.”

    If you’ve already set up one backup disk, Time Machine asks if you want to replace the existing backup disk or use both. If you already have multiple backup disks, Time Machine adds the new disk automatically without showing a confirmation message.

  6. If Time Machine prompts you to reformat the disk, either reformat the disk in Mac OS Extended (Journaled) format, or choose a different disk.

    Because reformatting erases any files on the disk, do this only if you no longer need the files or have copies of them on a different disk.

  7. If the Encrypt checkbox is available, you can select it to keep your backup disk secure.

    If the Encrypt checkbox is dimmed, your backup disk doesn’t support encryption.

    Encryption is available only for Time Capsules and for partitions or disks attached directly to your computer and partitioned with the GPT partition scheme. If encryption is not available for your disk, put the mouse pointer on the dimmed checkbox, and after a moment an explanation appears. If a disk needs to be reformatted or repartitioned to support encryption, Time Machine prompts you to do so.

  8. If you select Encrypt, type a password and password hint for the backup disk.

    After encryption is turned on, you’ll need to provide the password when you connect the backup disk to your computer. You will not need to provide the password again unless you disconnect the disk or restart your computer.

If you want to use multiple backup disks, repeat these steps for each disk.

Time Machine works best if you use your backup disk only for Time Machine backups. 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.

Published Date: Oct 20, 2015