Boot Camp problem, MBR, GPT

Question

Boot Camp problem, MBR, GPT

Hi!

So I got a 2011 MacBook Pro, running Yosemite version 10.10.2. The disk I'm using is a new "Samsung 850 EVO Series 250 GB" SSD.

I have tried using bootcamp to run Windows 8.1 on a partition of the drive. First I made a bootable USB from my ISO file with Windows and let boot camp make the partition and restart the computer. Once booted into Windows, the computer couldn't find the USB that boot camp made. I then restarted the computer manually while holding down the C button. I then chose to boot from the USB and the installation process started.

When I tried to formate the bootcamp partition to NTFS I got an error message telling me that Windows cannot be installed to this disk. The selected disk has an MBR-partition. In EFI-based systems Windows can only be installed on GPT partition disks (roughly translated from Swedish).

I then took a look on my disk using disc utility and from what I can read the disk is formated as an GUID-partition disk. If I understand correctly, GUID and GPT are the same, right?

Even though the disk seamed to be formated correctly, I booted the computer to recovery mode and tried to format the main disk once again. There I clicked on the the partition tab, chose options and then GUID. Then, when trying to format the disk i got an error message telling me that disk utility "couldn’t unmount disk".

What should I do now?

MacBook Pro, OS X Yosemite (10.10.2), Boot Camp

Posted on Mar 8, 2015 3:03 AM

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Answer 1

Loner T

Level 9

59,586 points

Mar 8, 2015 12:19 PM in response to pontusvargvik

Is your USB an USB3 or a USB2 device? USB3 will not work, because the Windows Installer (both, W7 and W8+) do not have USB3 drivers.

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Answer 2

Loner T

Level 9

59,586 points

Mar 8, 2015 7:59 AM in response to pontusvargvik

There are two methods of installing Windows on a Mac.

1. Macs that pre-date Late 2013, support a legacy BIOS method, which uses a GPT/MBR combination to install windows. This is called the Hybrid MBR method. This also uses a BIOS emulation method called CSM-BIOS.

2. Late2013+ Macs support a newer method using EFI boot, which works very well with W8+. This is because such macs are UEFI-compliant (EFI 2.0). Macs have used EFI 1.1 specifications till Late 2013 models which do not support EFI boot very well.

Depending on your Mac's year/model, an EFI boot may or may not work properly.

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Answer 3

Loner T

Level 9

59,586 points

Mar 8, 2015 8:24 AM in response to pontusvargvik

This is from a 2012 13" MBP.

The GPT and MBR are listed below.

sudo gpt -vv -r show /dev/disk0

Password:

gpt show: /dev/disk0: mediasize=256060514304; sectorsize=512; blocks=500118192

gpt show: /dev/disk0: Suspicious MBR at sector 0

gpt show: /dev/disk0: Pri GPT at sector 1

gpt show: /dev/disk0: Sec GPT at sector 500118191

start size index contents

0 1 MBR

1 1 Pri GPT header

2 32 Pri GPT table

34 6

40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B

409640 250392096 2 GPT part - 53746F72-6167-11AA-AA11-00306543ECAC

250801736 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC

252071272 664

252071936 248045568 4 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7

500117504 655

500118159 32 Sec GPT table

500118191 1 Sec GPT header

sudo fdisk /dev/disk0

Disk: /dev/disk0 geometry: 31130/255/63 [500118192 sectors]

Signature: 0xAA55

Starting Ending

#: id cyl hd sec - cyl hd sec [ start - size]

------------------------------------------------------------------------

1: EE 1023 254 63 - 1023 254 63 [ 1 - 409639] <Unknown ID>

2: AC 1023 254 63 - 1023 254 63 [ 409640 - 250392096] <Unknown ID>

3: AB 1023 254 63 - 1023 254 63 [ 250801736 - 1269536] Darwin Boot

*4: 07 1023 254 63 - 1023 254 63 [ 252071936 - 248045568] HPFS/QNX/AUX

The GPT is mapped 1:1 to a MBR in a Hybrid MBR for Macs which is the default. Notice that GPT1 start/size is the same as MBR1, GPT2 as MBR2, and so on. The mapping can be arbitrary, because MBRs are limited to 4 entries and a 2TB disk (32-bit LBA addressing).

If you need more details please see http://www.rodsbooks.com/gdisk/hybrid.html.

Can you post the output of the two highlighted commands? "sudo" commands require your password and may warn you about improper use and potential data loss, if "abused".

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Answer 4

Mar 8, 2015 8:43 AM in response to Loner T

Here is my output:

sudo gpt -vv -r show /dev/disk0

Password:

gpt show: /dev/disk0: mediasize=250059350016; sectorsize=512; blocks=488397168

gpt show: /dev/disk0: PMBR at sector 0

gpt show: /dev/disk0: Pri GPT at sector 1

gpt show: /dev/disk0: Sec GPT at sector 488397167

start size index contents

0 1 PMBR

1 1 Pri GPT header

2 32 Pri GPT table

34 6

40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B

409640 486717952 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

487127592 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC

488397128 7

488397135 32 Sec GPT table

488397167 1 Sec GPT header

sudo fdisk /dev/disk0

Disk: /dev/disk0 geometry: 30401/255/63 [488397168 sectors]

Signature: 0xAA55

Starting Ending

#: id cyl hd sec - cyl hd sec [ start - size]

------------------------------------------------------------------------

1: EE 1023 254 63 - 1023 254 63 [ 1 - 488397167] <Unknown ID>

2: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

3: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

4: 00 0 0 0 - 0 0 0 [ 0 - 0] unused

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Answer 5

Mar 8, 2015 8:09 AM in response to Loner T

I'm sorry but I don't fully understand.

Are you saying that GUID is a combination of MBR and GPT? If so, how do i proceed? As I said before, my MacBook Pro is from 2011.

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