Use Time Machine to Backup to an External Hard Drive

Ben Winters -

Learn how to set up Time Machine to perform backups, how to restore items, how to use System Restore to return your entire Mac to a specific date, how to migrate backups to a new Mac, and more.

Time Machine is the built-in backup that works with your Mac and an external drive (sold separately) or AirPort Time Capsule. Connect the drive, tell Time Machine to use it, and relax. Time Machine automatically backs up your entire Mac, including system files, applications, accounts, preferences, email messages, music, photos, movies, and documents. But what makes Time Machine different from other backup applications is that it not only keeps a spare copy of every file, it remembers how your system looked on any given day—so you can revisit your Mac as it appeared in the past. Time Machine keeps hourly backups for the past 24 hours, daily backups for the past month, and weekly backups until your backup drive is full.

OS X Lion lets you:

  • Encrypt your Time Machine backup drive using FileVault 2.

OS X Mountain Lion lets you:

  • Encrypt AirPort Time Capsule backups and network backups using FileVault 2.
  • Select multiple backup destinations that Time Machine will rotate through for backup cycles.
  • Complete backups when the Mac is in Power Nap (on compatible Macs).

Setting up Time Machine backups using an external drive

Setting up Time Machine is as easy as connecting an external drive to your Mac via Thunderbolt, FireWire or USB.

If you haven’t specified a Time Machine backup device and you connect an external drive, Time Machine will display a dialog similar to this one:

Note: The “My Backup (489.5 GB)” text in the above example, will be replaced with the name and capacity of the external drive you connect.

Click “Use as Backup Disk” to confirm you want to use the drive for Time Machine backups. Time Machine preferences will then open with this drive selected as your backup destination.

Check “Encrypt Backup Disk” if you want to encrypt the Time Machine backup external drive using FileVault 2 (OS X Lion and later).

That’s all you have to do for Time Machine to automatically backup your Mac. The Time Machine pane of System Preferences will look similar to this.

Note: The “My Backup” and drive capacity in the above example will be replaced with the name and capacity of the external drive you configured as your Time Machine backup.

Manually preparing a new disk for Time Machine

About the first backup to an external drive

You may want to set up Time Machine in the evening so that the initial backup can be done overnight because it may take a while depending on the size of your OS X volume. You should not interrupt the initial backup. You can continue to use your Mac while Time Machine backs up

Once the initial backup is completed, Time Machine performs subsequent hourly backups of only the files that have changed on your Mac since the last backup (as long as your backup drive is connected)

Tip: You can manually initiate a Time Machine backup cycle at any time by choosing Back up Now from the Time Machine menu, even if you have Time Machine preferences set to off

Manually selecting a backup drive

You can manually select a backup drive in the Time Machine pane of System Preferences.

Choose Time Machine menu > Open Time Machine Preferences…

If the padlock in the lower left is locked, click it and enter an administrator name and password to unlock.

Click Select Disk….

Select a drive, then click Use Disk.

Note: In OS X Mountain Lion and later, if a backup device is already selected, you will be prompted to click one of these options:

Cancel – This will cancel the process and leave your Time Machine settings as is.

Replace (current drive name) – Time Machine will stop using the current drive and replace it with the new selection.

Use Both – Time Machine will cycle backups through multiple backup devices. See the “Setting up an additional Time Machine backup (OS X Mountain Lion or later)” below for details.

Important: Every available drive that can be used to store backups is listed. If you’ve partitioned a drive, the available partitions are listed. Time Machine can’t back up to an external drive that’s connected to an AirPort Extreme or a drive formatted for Microsoft Windows (NTFS or FAT format).

If you select an NTFS or FAT-formatted drive, Time Machine prompts you to reformat the drive. Choose a different drive or reformat the drive in Mac OS Extended (Journaled) format. Because reformatting erases any files on the drive, only do this if you no longer need the files or if you have copies of them on a different drive.

The most common format for a Time Machine backup drive is Mac OS Extended (Journaled) format, but Time Machine also supports Mac OS Extended (Case sensitive, Journaled) and XSan formats.

If the drive is partitioned using the Master Boot Record (MBR) partition type, some partitions may not be available for use with Time Machine. The GUID Partition Table (GPT) type is recommended.

Time Machine works best if you use your backup drive only for Time Machine backups. If you keep files on your backup drive, Time Machine won’t backup those files and the space available for Time Machine backups will be reduced.

OS X Mountain Lion, OS X Lion v10.7.2 and later: Starting from the recovery partition of a Time Machine backup drive

Hold down the Option key at startup to boot into the startup manager. Select the Recovery system of the Time Machine backup to start from. Once started, you will have all of the functionality of Recovery.

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