Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

This disk is OCZ VERTEX 128GB SSD. It is formatted as GPT from OSX. The disk layout is,

   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *128.0 GB   disk1
   1:                        EFI                         209.7 MB   disk1s1
   2:                 Apple_RAID                         63.8 GB    disk1s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk1s3
   4:       Microsoft Basic Data ssdwin                  63.9 GB    disk1s4

I'm trying to install windows7 in the "ssdwin" partition but when i EFI Boot windows 7 64bit USB installer, it says,

Windows cannot be installed to this disk. The selected disk has a mbr partition table, On EFI system window can only be installed to GPT disks.

But my disk is GPT disk. any idea how i can recover from this ?

share|improve this question

1 Answer 1

up vote 17 down vote accepted

Did you happen to use Apple's Disk Utility to create a FAT filesystem in that to-be-Windows partition? If so, you converted the disk from a legal GPT disk into a hybrid MBR disk, which OS X sees as GPT and Windows sees as MBR. The solution in this case is to clear the hybrid MBR data. A number of utilities can do this. I'll describe how to do it with my own GPT fdisk (gdisk) utility:

  1. Download GPT fdisk from its Sourceforge page and install it. (Versions are available for Linux, OS X, and Windows. I'll assume you'll do this from OS X.) Alternatively, you could run it from a Linux emergency disc like Parted Magic.
  2. Launch gdisk on your disk by typing sudo gdisk /dev/disk1 in a Terminal window. (Change the device identifier if it's not as you presented earlier or if you use another OS for the job.)
  3. Type p to view the partition table to verify you're working on the correct disk. If not, type q to quit without saving your changes and try again with another device.
  4. Type x to enter the experts' menu.
  5. Type n to create a fresh protective MBR. Note that gdisk won't confirm a change; it'll just show you a new experts' prompt.
  6. Type w to save your changes. You'll be asked to confirm this action. Do so.

With any luck this will fix the problem. If it doesn't, though, you can use gdisk's v option (on any menu) to have gdisk look for partition table problems. It can fix some minor problems automatically, but other times you'll need to make explicit changes. See the GPT fdisk documentation on GPT repairs for details.

share|improve this answer
thank smith. This exactly the problem. i was experimenting with gdisk yesterday and after converting to protective mbr problem was solved. thanks for your details explanation and steps. and thanks again for creating nice utility gdisk :) –  Sarim Nov 21 '12 at 3:56
Rod, thank you so much for putting this up. I was having major issues with the same thing on a newly formatted 2013 Macbook Pro Retina. Couldn't get Win8 to install out of the box via the legit bootcamp Assistant method (I did not fiddle around with the disk utility). I still had the issue and following your tutorial to the T worked like a charm. Thanks again! You saved me a gzillion hours trying to get this to work. –  saurabhj Sep 8 '13 at 3:34
Thanks for this, after Ubuntu 14.04 grub messed up my Mac Pro with Mac OSX Yosemite Beta 2+Windows 8 Boot Camp, your gdisk steps made OSX and Windows bootable again. –  Erwin Coumans Aug 26 '14 at 3:25
If I understood correctly, these steps will delete existing partitions and destroy data (or maybe just Win partition?). Is it possible to perform this operation, but save the data on both Win and MacOS partitions? –  Dejan Mar 11 at 16:43
These steps destroy the hybrid MBR data, but the hybrid MBR merely duplicates (in MBR form) one to three GPT partition entries. The GPT entries remain intact and accessible, so you should not lose access to any of your files. Of course, all this assumes that the partition tables are valid (or as "valid" as any hybrid MBR can be). If your partition tables are damaged and your hybrid MBR specifies partitions that are don't have GPT counterparts, then you'll lose those partitions. This would be a highly illegal and dangerous setup at the outset. –  Rod Smith Mar 12 at 0:23

protected by DragonLord Jan 19 at 18:45

Thank you for your interest in this question. Because it has attracted low-quality answers, posting an answer now requires 10 reputation on this site.

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.