I have just got a new external hard disk, the Seagate Expansion 2 TB, and I am trying to format it to work on my Mac. I was told that I had to erase the disk and format it to OS X Extended (Journal) with the Disk utility program.

However, Disk Utility won't allow me to erase it, and the partition button is greyed out. I will attach some screenshots of the problem:

Partition button is greyed out This is the error message that pops up when i try to erase it

Any help is appreciated!

  • You may try formatting from the console. Here's the help topic for you: apple.stackexchange.com/questions/84098/…
    – Farside
    Apr 6, 2016 at 14:24
  • This looks to complicated for me to handle, hopefully i'll find another way. I don't wanna mess around with terminal unless there is no other option. Apr 6, 2016 at 14:37
  • 2
    @MatsSchibbye Did you try to choose the superior Seagate item and erase that one? Use the GUID scheme!
    – klanomath
    Apr 6, 2016 at 14:39
  • @klanomath, is it the thing I outlined in the answer, right? to select the HDD, not the friendly name that appears under it?
    – Farside
    Apr 6, 2016 at 15:34
  • @farside Yeah that's it . But I didn't read your answer completely because of the 1st sentence. You can always format and erase mounted drives except they contain a lot of important open files (e.g the boot volume).
    – klanomath
    Apr 6, 2016 at 15:44

1 Answer 1


In Disk Utility find the HDD you are trying to format in the left hand column. Select the disk and not the volume - that appears as child under it - to repartition it.

Just choosing the volume erases or replaces the file system but not the partition table type. This may apparently fail if the partition map is mal-formed.

enter image description here

If you feel confident with terminal, you may use instructions from other topics, alike this one.

  • I tried un-mounting the hard drive, it still won't let me press the partition button, or erase the disk. I don't know a thing about terminal, so hopefully i'll find another solution Apr 6, 2016 at 14:35
  • which row do you try to select? please, find out my edited answer.
    – Farside
    Apr 6, 2016 at 14:35
  • Looks like the one on top will let me erase, so do i choose GUID partition map, Apple partition map, or Master boot record? I will only use it on my mac and only need one partition Apr 6, 2016 at 17:33
  • @MatsSchibbye, feel free to up-vote and accept the answer, as it appears to help you to solve the issue. Thank you, welcome!
    – Farside
    Apr 7, 2016 at 8:06
  • @klanomath, I removed the redundant texts, which probably would not be helpful. thank you for the corrections! It seems this input helped the guy to solve his issue, and this is good
    – Farside
    Apr 7, 2016 at 8:09

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