Using Time Machine to back up an external drive

Whether you are working with thousands of photos, hours of video or semesters of lesson plans, securing and backing up your data remains critically important. If you have all of your data stored on the hard drive in your computer, this can be as easy as plugging in an external drive and setting up Time Machine (on a Mac). More likely, if you work with a lot of photos and video like I do, you have most of your data on an external drive. In an ideal world, you would back these up using some sort of Network Attached Storage RAID array. Coming from a newspaper environment, I know this isn’t always a reality. Sometimes all you have are a few externals lying around. Did you know that you can also set up Time Machine to back up one external drive (a media drive or capture scratch for example) to another external?


To do this, we will first go to our Apple Menu Items in the top left, and select the System Preferences. From there, open up Time Machine. Once in the Time Machine preferences panel, click on “Select Disk…” and choose the drive that will serve as the Time Machine backup.


Next, click on “Options…” in the lower right corner. This will bring up a window showing you what drives are excluded from the backup process. By default, your external drives will be here. Your backup drive is automatically excluded from the backup process, as it wouldn’t make sense to back it up to itself. However, we DO want to backup the Media drive, so let’s remove it from this list by selecting it and hitting the minus symbol as shown below.


As currently configured, Time Machine will try and backup the Media drive along with any internal hard drives. But we only want to backup the external Media drive, so let’s add our internal drives to this exclusion list. Click on the plus sign next to the minus sign you used earlier, and then find and exclude your internal drives.


In my case, I have two internal drives that I needed to exclude from Time Machine backup. Once complete, you can hit “Save” and then turn on Time Machine.


12 thoughts on “Using Time Machine to back up an external drive”

  1. This does not work since I have a Mac (3 years right now) because all external drives cannot be added or removed in Time Machine options.

  2. Thanks Daniel, a really useful article. I have a situation where I would like to do both, backup an internal drive and backup from the Airport Time Capsule to an external HD (effectively back up the back up!). Is this possible to configure on Time Machine?

  3. That’s exactly what I wanted to know, except I cannot select the USB hard disk to remove it from the excluded list. My cursor will not select it, it remains greyed out. Ideas?

  4. Hey Daniel – thanks for taking some time to write this up. I’m using Yosemite and am unable to remove the external drive I want to back up from the exclusions list.

    Have you encountered this before?

  5. Hey, Daniel!

    I just wanted to say thanks for the tutorial. Super helpful.

    Miguel Monroy

  6. The minus (-) sign is greyed out for me as well. How do I fix that so that I can backup my external drive? Thanks

  7. Thanks for video. But what about the following:

    Mac mini with 120SSD +iomega mini max 2T

    one Time Capsule 2T

    Can I use Time C to back everything up, or is better set up just use to back up the iomega, so make sure all sensitive media kept on ioemga mini max, and just keep applications and OSX on SSD drive.

    Think I answered my own question !!! just keep a bootable version of El Capitain at hand, and make sure all settings are saved in Apple iChain.

  8. I have a 1TB external drive that is now full. I bought a new one to continue. If I plug it in will it back up everything again? If so will it fill up right then? What do I do? How do I start where it left off and should I do that. ? Thank u
    Nancy G.

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