I just bought a new external hard disk and I want to create some partitions. I am using the Disk Utility app in an High Sierra OSX MacBookPro.

However, the "partition" option for my hard drive is greyed out, therefore I cannot go ahead with the partition operation.

enter image description here

Although, when issuing the command diskutil partitionDisk disk2 2 MBR fat32 "PART1" 80% fat32 "PART2" 20%, I am able to partition, I cannot directly operate through Disk Utility.

How can I do this using the Disk Utility application?

  • It's a little vague here just based on the picture. What happens if you issue the command (in Terminal) diskutil partitionDisk disk2 2 MBR fat32 "Part1" 80% fat32 "Part2" 20% Post the results to your question.
    – Allan
    Mar 13, 2018 at 12:06
  • @Allan When issuing the command diskutil partitionDisk disk2 2 MBR fat32 "Part1" 80% fat32 "Part2" 20%, the following message is displayed: "Part1 does not appear to be a valid volume name for its file system".
    – mgiordi
    Mar 13, 2018 at 12:09
  • oops...make them all caps (i.e. "PART1")
    – Allan
    Mar 13, 2018 at 12:11
  • OK now I see the two partitions, but still I cannot operate directly through Disk Utility.
    – mgiordi
    Mar 13, 2018 at 12:14
  • 1
    @dwightk - if it does get closed, having both names will give it two vectors to be found as this one will link to the target.
    – Allan
    Mar 13, 2018 at 18:00

2 Answers 2


The Disk Utility application can partition the external drive, if you use GUID Partition Map scheme.

Below is an example using a 16 GB flash drive.

  1. Erase the drive.


  2. Partition the drive.


  3. Erase the first partition.


The results are shown below.




  • Also works on Mojave
    – marlo
    Mar 12, 2019 at 1:29

Try formatting the drive as either APFS (if an SSD) or MacOS (Extended, Journaled if spinning drive). MBR is a windows technology and has various limitations on MacOS.

If it needs to be MBR, try renaming the drive to have <11 characters in the name as per the official documentation:


  • The partition button is greyed out and unavailable (from screenshot). Also, TOSHIBA_EXT is exactly 11 chars which qualifies.
    – Allan
    Mar 13, 2018 at 13:08
  • The definition of a MBR existed before there was a Windows technology. Many other operating systems written by many other companies use the MBR. Apple's macOS requires an MBR. Mar 13, 2018 at 23:23

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