How To Partition USB Drive macOS High Sierra

Time required: < 10 minutes

To partition USB drive macOS High Sierra can be a useful way to organize your data on an external hard drive. Problem is, most USB keys and external hard drives come formatted for Microsoft Windows and have what’s called a Master Boot Record. By default, you can’t view the options to enable you to change this in macOS’s Disk Utility to be able to change it to the standard GUID partition: this is what allows you to create partitions on a USB drive or external hard drive.

Typically the Partition button will be greyed out, and on hover the following message will be displayed: “Disks with master boot record cannot be partitioned.”

Partition USB drive macOS High Sierra, choose View and select Show All DevicesFear not, however, for we have found the solution:

In Disk Utility, Select View and tick Show All Devices. This unhides the containers where you can select to Erase (format) a drive with a GUID Partition table. Follow along for the full guide on how to partition a USB drive in macOS High Sierra.

Partition USB Drive macOS High Sierra

Things you will need:

  • A Macintosh computer running macOS High Sierra (10.13) or higher.
  • A USB key (any size GB is fine) OR
  • an external hard drive (USB or otherwise, any size GB will work).

WARNING: This process will have you format the USB drive or external hard drive, which means you’ll lose all existing information on that drive. Triple-check that there’s no data on the drive that you want to save, if there is, you will have to move it somewhere else before you continue. You’ve been warned.

Part 1: Prepare USB Drive

If your drive is already formatted as GUID Partition Map and you can see containers in the sidebar, you can skip to Part 2: Partition USB Drive.

  1. Plug in your USB key or external drive to your computer.
  2. Guide: Partition USB Drive macOS High Sierra, steps A, B, CLaunch Disk Utility. Press CMD + Spacebar to search for it or go to Applications > Utilities > Disk Utility in Finder.
  3. In the upper left corner of Disk Utility, select View (A) and tick the option Show All Volumes. Your sidebar should now show a parent field for your USB drive or external hard drive. Select this parent (see screenshot).
  4. With your USB drive or external hard drive selected (B), click Erase in the toolbar (C).
  5. Guide: Partition USB Drive macOS High Sierra, steps D, EIn the window that pops up, for Scheme select GUID Partition Map (D).
    • Name: You may give your drive a new name (this is how it will be shown in your computer later on.
    • Format: if you need the drive to work on both Macs and PCs, select ExFAT. Otherwise Mac OS Extended (Journaled) is your best option.
  6. Click Erase (E) to begin reformatting. Depending on your drives size this may take a few minutes.
  7. Click Done when complete. Now your drive is ready to be partitioned, see Part 2 below.

Part 2: Partition USB drive macOS High Sierra

If your USB drive is formatted as GUID Partition Map, the Partition button should now no longer be greyed out.

Partition USB macOS High Sierra: Part 2, partitioning steps A, B

  1. Select your drive in the sidebar (A) and click Partition (B).
  2. Partition USB macOS High Sierra: Part 2, partitioning steps C, D, E, FIn the window that opens, use the + and - buttons in the lower left corner (C) to add and remove partitions. Give each partition you want to add a name (D) and set its size in GB (Gigabytes) (E). You can also drag the dots around the circle representing your drive to change the size of each partition.
  3. When you’re happy, click Apply (F) and then Partition in the popup window. Your partitions will be created, this may take a few minutes.
  4. Click Done when complete.
  5. That’s it! Your new partitions will be mounted on your desktop and appear as separate drives in macOS High Sierra.

Were you able to partition USB drive macOS High Sierra?

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6 Responses

  1. Al says:

    Selecting the Parent Field on the USB drive is the trick. I missed this the first time and downvoted. I would upvote now. My mistake!

  2. Akshat says:

    This volume cannot be resized on 8gb usb

  3. John says:

    What did you use to write your page? I’d like to markup my screenshots with the A, B, C… and then use the same A, B, C graphic in my writeup. Thanks

  4. Tata says:

    Repeated it a couple of times, but the result is always:
    Applying changes to “CARDER READER Media”
    Operation failed…
    Fail system check failed

    • Admin says:

      You may have a faulty drive on your hand. Try running diagnostics to see if there are any errors and/or formatting the drive (WARNING: formatting will permanently remove and and all information on your drive, do it at your own risk!)

  1. October 15, 2018

    […] the USB key to have two partitions. Ok, this isn’t super clear, but with a Mac, you need to reformat your USB key to use the GUID Partition Map. You do this by loading your USB key, and then choosing Erase Disk and tell it you want a GUID […]

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