Install Windows dual-boot to Mac Pro using OWC SSD

Usually setting up a dual-boot for Windows on a Mac is a fairly straightforward procedure—use Boot Camp Assistant to create the USB installer and then have Boot Camp Assistant help you set up the partitions and install Windows.

We ran across a rather odd scenario with some Mac Pros, whose internal storage we'd upgraded from the built-in storage to the Aura SSD. The SSD uses the PCIe interface but seems to use that as an intermediary for the larger SSD attachment, which Mac OS X sees as an external drive, and Bootcamp does not like to install to an external drive.

This may not be the only approach that works, but it seems to have worked for us:

  1. Set up your .iso and USB stick as you normally would in Mac OS X using Boot Camp Assistant. If you get an error that says You cannot partition an external disk, a RAID disk or an internal disk on which FileVault encryption is in progress, ignore it. Yes, you're using an external disk, but right now you're not partitioning. You're just setting up the USB stick.
  2. Use Disk Utility to make a second partition that's MAC OS (journaled). (Don't make a FAT32—when I did, the Windows installer complained.)
  3. Keep the USB stick plugged in.
  4. Download rEFInd, and after you extract it, run
    sudo /Users/username/Downloads/refind-bin-versionnumber/refind-install
    Note: this command won't work in El Capitan unless you disable SIP first.
  5. Reboot and pick the Windows installer from the list of bootable drives. You'll likely see three options (Boot Fallback boot loader from NAMEOFUSB, Boot Windows from whole disk volume, and Boot Windows from NAMOFUSB). If you try the latter two, you'll get Error: Not Found while loading legacy loader. So, instead, you want to select Boot Fallback boot loader from NAMEOFUSB.
  6. When you get to the Where do you want to install Windows? part of Windows Setup, you'll see your Mac OS (Journaled) partition with a warning like Windows can't be installed on drive 0 partition 4. (Show details). If you click on the details, it'll say Windows cannot be installed to this hard disk space. Windows must be installed to a partition formatted as NTFS. Windows cannot be installed to this hard disk space. The partition is of an unrecognized type. In other situations (internal drive, Windows 7), I've been able to get around this by formatting the partition as FAT32 in advance (but when I did that with an "external" drive and Windows 10, I got an error of Windows cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GPT disks). So select the partition (e.g., Drive 0 Partition 4) and then click Delete. Then click on the Drive 0 Unallocated Space that freed up, and then click New and then Apply. You'll see that Windows Setup created a small 16 MB "MSR (Reserved)" partition and then another, much larger (NTFS) partition.
  7. During installation, you may get an error like this: windows10installerror If you do, just let it go through. I had that happen a couple of times on one Mac, once on another, and not at all on a third. They seem to be fine. I'll update this post if that proves not to be the case.
  8. Windows should install fine after that. If you get a weird situation in which Windows boots up okay but hangs when rebooting, install all Windows updates and Boot Camp updates as well.

9 thoughts on “Install Windows dual-boot to Mac Pro using OWC SSD”

  1. 1. Boot Fallback boot loader is not there.

    2.Mouse/Keyboard is not appearing during windows 7 installation.

    3.Do you think this method would work with (MBP Late 2013 Retina OWC SSD)?

  2. 1. It doesn’t really matter if it’s not there. Did you install rEFInd and have boot options? Pick the one that makes sense for your situation. I just said that if you get three options, you should pick that one of the three because the other two won’t work. If you get only one option, pick it.

    2. That’s a completely separate issue, and it’s a common problem. Lots of potential solutions:
    https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=windows%207%20installer%20keyboard%20mouse%20bootcamp

    3. I would not recommend this method at all. This method is for a very specific set of circumstances—installing a dual-boot on a Mac Pro 2013 that has an OWC SSD drive installed. If you’re using a regular MacBook Pro, just use Boot Camp (don’t even bother with rEFInd) and go through the Boot Camp wizard:
    https://www.apple.com/support/bootcamp/

    1. The mouse won’t work if it is connected to a USB port on an Apple keyboard while trying to install Windows, as Windows driver dont give the USB ports enough power, so connect to a USB port on the front or rear of the Mac Pro.

    2. Emant, I am also a MBP Retina Late 2013 OWC SSD and continue to have issues getting windows 7 installed on my system. Have you made any progress since your last post?

  3. This method worked for me – THANK YOU! I had almost given up trying. I bought an OWC Aura 1.0 TB SSD for my MacBook Pro Retina 15″ Late-2013. I didn’t realize that the MBP would see the Aura as an external drive.

    Using my original OSX install (on the drive that came with the MBP), I downloaded the Windows 10 ISO file and created the USB stick with the Windows 10 Install & Bootcamp Drivers. Then I also downloaded the OSX El Capitan installation file and loaded it to a USB stick.

    I installed the new OWC Aura into my MBP, then I installed El Capitan. Then I followed your directions above, and it worked!

    Great workaround, and thanks for the tip about rEFInd!

  4. I would test it. See if you can boot to your Windows partition by holding down the Option key at startup. If so, you will no longer need rEFInd (which will be disabled after any major upgrade to OS X), and you can safely re-enable SIP.

  5. Finally, succeed installing my windows 10 using your method, but Windows 7 cannot be installed since Windows 7 needs a separate hardware driver package and this package cannot be detected during the installation stage. Thanks for your post. You help me learn a new skill.

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