Yosemite, bootcamp and huge disaster

zumbito

macrumors newbie
Original poster
Jun 25, 2015
5
0
So I decided I needed windows in order to run some programs in my Imac late 2011. Then problems started:

1- OS didn't offer me the option of booting from a USB -- Solved
2- When created the boot USB, the computer didn't recognize a bootbale USB when restarting --- I solved it too
3- When the Boot USB was detected and started installing windows an error message came up when I chose the bootcamp partition, saying that is was MBR and windows can only install on GPT.--- And here everything went wrong.

I saw a video on youtube showing a way to install windows, by cpressing shift+f10 then run diskpart on the console (all this in the windows installer) and then chose the disk and have it changed from MBR to GPT, and so I did. Everything worked flawlessly, but apparently the change from MBR to GPT was not only on the partion but the entire HDD, and OSX has disappeared.

I've tried booting pressing option, but only the windows EFI partion appears. If tried booting internet retore and nothing happens, and I don't know what else to do. I really need help.
Has anyone gone through the same or knows how to solve it? Preferably without wiping my OSX files.

Thanks a lot.
 

yjchua95

macrumors 604
Apr 23, 2011
6,725
230
GVA, KUL, MEL (current), ZQN
So I decided I needed windows in order to run some programs in my Imac late 2011. Then problems started:

1- OS didn't offer me the option of booting from a USB -- Solved
2- When created the boot USB, the computer didn't recognize a bootbale USB when restarting --- I solved it too
3- When the Boot USB was detected and started installing windows an error message came up when I chose the bootcamp partition, saying that is was MBR and windows can only install on GPT.--- And here everything went wrong.

I saw a video on youtube showing a way to install windows, by cpressing shift+f10 then run diskpart on the console (all this in the windows installer) and then chose the disk and have it changed from MBR to GPT, and so I did. Everything worked flawlessly, but apparently the change from MBR to GPT was not only on the partion but the entire HDD, and OSX has disappeared.

I've tried booting pressing option, but only the windows EFI partion appears. If tried booting internet retore and nothing happens, and I don't know what else to do. I really need help.
Has anyone gone through the same or knows how to solve it? Preferably without wiping my OSX files.

Thanks a lot.
You're screwed. The moment you converted the whole thing to GPT, everything in OS X got nuked.

Keep in mind that you cannot install Windows in UEFI on Macs that are Ivy Bridge or older. You also cannot use the EFI Boot installer on such Macs, as EFI Boot will only install onto GPT disks.

Boot Camp Assistant on these older Macs formats the Windows partition as FAT32 first to be visible to the installer. BCA on these Macs will format FAT32 as hybrid MBR, where it appears as GPT to OS X and MBR to Windows.

Your biggest mistake was that you probably booted into the EFI Boot partition of the bootable Windows installer. The moment you GPT'ed everything, you screwed the entire drive.

Your only way is to boot into Recovery, open Disk Utility, reformat the entire drive as Mac OS Extended Journaled (yes, you'll have to remove Windows first before you can reinstall OS X) and then reinstall OS X.

The mistake started from step 2 onwards, assuming that you created an EFI boot disk.

The reason why UEFI Windows won't work on anything older than Haswell is because these Macs use EFI 1.1, while Haswell and later Macs use a custom implementation of UEFI 2.0 (where all of UEFI 2.0 is incorporated, along with some additional custom stuff).
 
Last edited:

MagicBoy

macrumors 68040
May 28, 2006
3,845
842
Manchester, UK
GPT or MBR is for the entire physical hard drive, not the partition. That's why it's broken.

The iMac Mid-2011 will support Internet Recovery if it had all the updates (inc the EFI) installed, otherwise you'll have to go back to the grey recovery disk to repartition the drive, install Snow Leopard then upgrade to Yosemite from there.

Hopefully you've learned from this to be very careful with diskpart! It's the reason that Apple bundle Boot Camp Assistant to setup the drive so you can't bork it using Windows tools that don't understand Mac file systems.
 

yjchua95

macrumors 604
Apr 23, 2011
6,725
230
GVA, KUL, MEL (current), ZQN
Yes.how do I do that? BTW will I loose all my data?
First, open Mac App Store on that Mac and download the Yosemite installer.

Then, use DiskMakerX (free app from http://diskmakerx.com) to create a bootable USB stick (use an 8GB stick). The app will walk you through it.

After that, stick the USB into the iMac and then start it up while holding Option/Alt. Boot into the USB stick, open Disk Utility and reformat the entire drive. Then reinstall OS X.

You already lost all your data the moment you converted the partition table into GPT from the Windows stick.
 

zumbito

macrumors newbie
Original poster
Jun 25, 2015
5
0
Oook, I'll have to live with that. Hope I can use bootcamp right this time.
 

yjchua95

macrumors 604
Apr 23, 2011
6,725
230
GVA, KUL, MEL (current), ZQN
Oook, I'll have to live with that. Hope I can use bootcamp right this time.
Just make sure you keep a Time Machine backup next time.

The next time you do it, use Boot Camp Assistant and install using the optical drive. If you stick to BCA, you will never go wrong.

Some people try to 'outsmart' the system and try installing Windows themselves (i.e. by formatting with Disk Utility instead) and then end up screwing everything instead.