I'm facing a little big problem concerning my windows partition: State of the art is, that I removed my CD-Drive and replaced it with a second SSD. Therefore I thought of moving windows 10 to one disk and leave os x on the "main drive" might be a good idea (just in case of possible future drive problems to fix them more easily). Although, Mac lists them both as internal drives, I firstly wasn't able to install it via Bootcamp on the second drive, so I installed windwos without Bootcamp directly on the drive using efi boot. Unfortunately efi boot isn't completely supported on this MBP model, (soundcard and TB2 for external displays don't work) but at least everything else worked that way! This is why I turned the efi boot into a bios boot. It worked perfectly, when only the drive with windows was inserted but when I added the second drive with os x, suddenly booting into Windows wasn't possible anymore! I did a little research and found out, that windows obviously needs to be on the "first" drive (disk0) to start. So, I shuffled the SSDs and was immediately able to boot windows again. Happy that I finally reached my goal I switched to os x. But when I tried to boot back into windows it didn't work again. I tried to recreate the boot files for windows with "bcdboot" and also created a startup partition on the os x drive of 200MB with the windows boot files but it's still not working. So now I don't know what to do anymore! I don't want to shuffle (or unmount) the disks every time I want to use windows! Is there a possibility to do a work around for that problem? (A virtual machine is no possible solution as I'm in need of full RAM capacity). Thanks in advance!

  • Both SATA chipsets do support 6 Gigabits, I already checked that! – Hecknub Dec 6 '18 at 10:58
  • After swapping OS X drive was disk1, but it was still not working. The interesting thing is, that when I use a boot stick for Windows, the numbers of the drives are swapped, so diskpart shows the Windows drive as disk1 and OS X as disk0... – Hecknub Dec 6 '18 at 11:05
  • And concerning the boot files: I have tried all three combinations to locate the boot files on either the Windows or the OS X drive as well as on both drives simultaneously. – Hecknub Dec 6 '18 at 11:09
  • Ok, thanks for the advice... I just created a bootable drive with dd command and tried to use rEFInd but something obviously went wrong because when I selected rEFInd in the startup, I just got a white screen with the logo but no systems to select... but I'm working on that! No, my problem is, that I just can't boot it. After selecting windows there's just a blackscreen with a white underline flashing! – Hecknub Dec 6 '18 at 12:27
  • I don't know if I have done that, maybe accidentally, but I've no idea, where to check that... second, I didn't but it didn't change anything! Third, I tried that using your instructions from the Link but still I'm not able to boot Windows, when the os x drive is mounted. – Hecknub Dec 6 '18 at 21:12

Below is a excerpt From page 6 of the Boot Camp Installation & Setup Guide (Copyright 2011). These instructions do change significantly with the next release of the Boot Camp Installation & Setup Guide (Copyright 2013).

If you have a Mac Pro with more than one internal disk and you want to install Boot Camp on a disk that isn’t in the first hard drive bay, remove the drives in the lower numbered bays. You can reinstall the drives after you install Boot Camp.

Back in 2011, all Macs were still BIOS booting Windows. Although the excerpt does not explicitly say Mac Pro's where the only models that could BIOS boot from a second internal drive, this was already generally known to be true. So, the answer to your question is your 2012 MBP can not natively BIOS boot from the second internal drive.

rEFInd is a Boot Manager. This means rEFInd does not actually boot operating systems. Instead, rEFInd saves information in the nvram. The Mac firmware reads this information to determine which operating system to load. The means rEFInd can to be directly used to BIOS boot windows from a second internal drive.

On the other hand, GRUB 2 is a boot loader. You may be able to BIOS boot GRUB on the primary drive and configure GRUB to boot Windows on the second internal drive.

  • Ok, I don't think, it makes a big difference, when WIN ist currently 'disk0' and OS X 'disk1' or should I Switch the drives again? At least when I follow your instructions, I get more or less the same output in terminal you showed. Also, I installed rEFInd now directly in the Mac Startup and I now do see an image the boot files for Win on each drive and the partition with the windows Installation. But it is still not working. Do you have any recommendations for a completely new Setup of the win disk? – Hecknub Dec 7 '18 at 9:19
  • Ok thank you. I will try to use that! But up to now I haven't figured out, how to install it properly. Do you have experience using GRUB 2? – Hecknub Dec 7 '18 at 13:52

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