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How-To: Transfer Time Machine BackUps or Add Extra Drives to Time Machine

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Time Macine

If there’s one thing that is entirely superior about Macs over PCs on other platforms, in my opinion, it has to be Time Machine.  Plug in an external drive, and macOS automatically asks if you want it to be a backup drive.  When you say yes, macOS automatically backs up your entire Mac every hour on the hour to ensure that all your data and all your apps are restorable should the worst happen and your Mac tanks and you have to rebuild it. Thankfully, Time Machine backups can save your bacon.

According to Apple, 

Time Machine backs up your computer and keeps local snapshots and hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for all previous months.  The oldest backups and any local snapshots are deleted as space is needed.

Given the above, the larger the drive you have, the better your RESTORE options when it comes time to put the world back together should you have issues with your Mac.  So, the more backup data you have, the easier it is to restore to a state before the world twists sideways.

So, having a huge drive – 10TB or larger – isn’t crazy and unreasonable, given that the more space you have, the better your restore options will be.  They’re also cheaper than SSDs and perfectly reasonable for backup media. 

Upgrading/replacing backup drives for Time Machine is – believe it or not – silly.  You don’t need to upgrade and replace a Time Machine drive.  All you need to do is add to your existing backup drive setup.  Not only do you get the benefits of keeping the original drive and all of its space, but Time Machine will incorporate any new space into the backup process, allowing you to maintain and keep all of your existing backup history.  Time Machine is set up to do this automatically, and the process is so simple two chimpanzees and a Star Fleet Trainee can do it blindfolded.

To add a (or another) drive to Time Machine, follow these steps:

First Time Activation

  1. Disable Time Machine from its menu item or via the Time Machine system preference pane.
  2. Connect your designated backup drive to your computer and allow the machine to recognize or “mount” it.  
  3. Launch Disk Utility.  Ensure that the drive is formatted according to the following two steps.
  4. Click the new drive’s icon in the left bar, and make sure the Partition Map is shown in the description to the right as GUID Partition Map.
    Disk Utility: GUID Partition Map

    Disk Utility: GUID Partition Map


  5. Click the drive icon to ensure the drive’s details match Time Machine’s requirements.


    Disk Utility: Drive Setup

    Disk Utility: Drive Setup


  6. If the drive details don’t match Time Machine’s requirements, click the Erase icon and set the following options:
    1. Name: Pick an appropriate drive name.  This is entirely at your discretion.
    2. Format: macOS Extended (Journaled)
    3. Partition Map: GUID Partition Map
  7. In the Finder, select the drive and choose File > Get Info.
  8. Uncheck the box Ignore Ownership of This Volume if it isn’t unchecked (in the Sharing & Permissions section). You may have to click an expansion triangle to open it, and you may need to click the lock icon in the window’s lower right corner to access the check box.
    Get Info: Ignore ownership on this volume

    Get Info: Ignore ownership on this volume.

  9. When finished, open the Time Machine system preference pane and click Select Backup Disk.
  10. Select the new disk in the list and click Use Disk.  You should be prompted to re-enable Time Machine; if not, flip the switch back on.

Adding an Additional Drive to your Backup Array

Adding an additional drive to Time Machine is very easy.  The benefit of having more than one drive here is that your backup space expands. Time Machine will automatically alternate backups between your drives and manage the space to maximize the benefit of that additional space.

To add an additional drive to Time Machine, follow these steps:

  1. Follow steps 1-8 above to prepare your intended backup drive for use as a Time Machine backup drive.
  2. Open Time Machine Preferences and then tap the “+” at the bottom left corner of the available drives window


    Add drive to Time Machine

    Add drive to Time Machine.


  3. In the subsequent window, select the disk you wish to use and tap the Setup Disk button.
    Time Machine: Setup Disk

    Time Machine: Setup Disk

  4. Choose if you want to encrypt the backup on this drive in the resulting window.  Please remember the following if you decide to do this:
    1. If your backups aren’t encrypted on your other drives, don’t encrypt them here.
    2. Keychain won’t remember this password.
    3. If you encrypt your backups and forget this password, you won’t be able to restore your Mac from the array (group of drives), and their contents are useless.
  5. Choose if you wish to limit Time Machine’s use of disk space on this drive, and then define how much space Time Machine may use.  I usually do not recommend this.  Let Time Machine have the drive.  You won’t regret using the entire drive for backups and will be glad you have the space if you ever decide to blow your Mac and restore from a backup.
    Time Machine: Encrypt & Limit Disk Space

    Time Machine: Encrypt & Limit Disk Space

  6. Click Done to add the drive to the array.  Time Machine will run through a process that prepares the drive for Time Machine’s use.
    Time Machine: Preparing Drive

    Time Machine: Preparing Drive

  7. When completed, you’ll have an extra drive added to Time Machine and that much more protection.
    Time Machine: Drive Added to Array

    Time Machine: Drive Added to Array

You can never have too much backup space.  Saving memories like pictures, videos, documents, etc., may be handled by a cloud backup service like iCloud/iCloud Drive, but those services don’t save your computer settings or apps.  Rebuilding your PC can be a pain, and having something that backs up not only your data but also your Mac’s apps and machine settings can be a massive help if you ever have to reset it and “start from scratch.”


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