This is really annoying. I have a brand new Seagate 3TB 7200 RPM hard drive that I am trying to format/partition in Disk Utility. Every time I change any settings or erase the drive, it changes it to a Logical Volume Group and subsequently changes the partition to a Logical Partition. Then I have to use Disk Utility in terminal and manually erase it.

This is really weird because I have two of these exact same drives and I zeroed out and partitioned the first one a couple of months ago without any issue whatsoever. I am not doing anything different than I always do when setting up my HDs.

I'm running OSX 10.8.4 on a 2009 Mac Pro.

Edit: I am not trying to make a Fusion Drive. The drive will be partitioned as GUID Partition Table with 1 partition and Mac OS Extended (Journaled) and then when I erase the drive or change the number of partitions, or the partition map—any of these adjustments makes it instantly a Logical Volume Group. Again, to clarify, this is ONE drive, I shouldn't be able to make it a fusion.

  • Are you somehow trying to make a Fusion drive? Can you clarify "it changes it"? A screenshot may help.
    – duozmo
    Commented Jun 19, 2013 at 2:17
  • @Aphex5 I updated my question.
    – daveMac
    Commented Jun 19, 2013 at 16:10
  • Do you have FileVault turned on for that drive? Filevault works using Logical Volumes.
    – 8None1
    Commented Jun 19, 2013 at 16:15
  • @8None1 No, FileVault is not turned on.
    – daveMac
    Commented Jun 20, 2013 at 16:47
  • This issue has come when using Disk Utility on a MacPro in both Mountain Lion (10.8) and Mavericks (10.9). For another solution using a Snow Leopard (10.6) install DVD, see my answer here on AskDifferent.
    – GrowlTiger
    Commented Jan 20, 2014 at 20:26

3 Answers 3


I also have this issue... MacPro, 3TB drive (Seagate). I have to use the terminal:

diskutil list
diskutil unmount /dev/disk22
diskutil eraseDisk HFS+ "Macintosh HD" /dev/disk22

etc etc to utilize this drive correctly. (Sorry for all the commands. Posting them just in case it helps someone. Though anyone using those commands better know what they do first!)


I've had the same problem with a 3TB Barracuda and a 3TB Deskstar. The only fix was to delete the logical volume diskutil CS in the terminal.

Also running 10.8.4 on a 2009 Mac Pro (upgraded to macpro5,1 firmware).

  • I believe this is a bug with 3TB Hard drives in the later updates of Mountain Lion. Since my original post, I have tried other sizes without any issue.
    – daveMac
    Commented Aug 6, 2013 at 16:49
  • I've also had this problem with Toshiba 3TB drives, erased via both Disk Utility and CLI diskutility.
    – Elliott
    Commented Sep 3, 2013 at 18:29

I have figured out a solution to this issue.

Here are the steps:

  • Go to Apple menu > About This Mac, click on More Info and then System Report and go to Storage. Get the UUID of the volume from here (an example of a UUID is 8DD219E1-AA47-4F4C-A9DF-72BE79143B43).
  • Open Terminal.app and enter the following:

    diskutil cs delete [Put Your Logical Volume Group UUID Here]
  • By following the steps right above, if I enter the diskutil cs delete [Put Your Logical Volume Group UUID Here], will this delete the other 2 partitions that is part of this drive? Those 2 partitions seem to be fine. The only one with a Logical Volume Group is the one partition of 3. Thanks...
    – user96462
    Commented Oct 19, 2014 at 21:06

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