Home > Mac administration, Mac OS X, Windows > Unplug USB and Thunderbolt devices when setting up Windows 8.x or 10.x using Boot Camp on OS X El Capitan

Unplug USB and Thunderbolt devices when setting up Windows 8.x or 10.x using Boot Camp on OS X El Capitan

As part of setting up a dual-boot configuration for a group at my shop, I was working with a colleague to set up a new Windows 10 installation using Boot Camp on a new Retina MacBook Pro. As part of the process, we did what we normally did and plugged in a USB flash drive to store the Windows installation files on.

The Boot Camp Assistant asked for the location of the Windows 10 .iso file, proceeded to repartition the disk, then rebooted into the Windows install process. When prompted where we wanted to install Windows, we selected the BOOTCAMP partition and clicked Format.

At that point, Windows formatted the drive. So far so good. We then selected the drive, clicked the Next button, and received the following error:

We couldn‘t create a new partition or locate an existing one. For more information, see the Setup log files.

Partition Error On Windows Install 01

Our thought at that point was that something had gone wrong with the format, so we booted back to OS X, had Boot Camp Assistant remove the Windows partition and tried again.

Same result, same error.

We went back to the Boot Camp documentation and read it over carefully. There is a note about unplugging Thunderbolt devices, but we didn’t have any plugged in.

Screen Shot 2016 09 02 at 1 42 21 PM

So we tried again, starting over from scratch. Same result, same error.

After some additional research, we finally found the answer: The note should have read “Thunderbolt or USB storage devices”. This additional information is included in an Apple KBase article for installing Windows 8 using Boot Camp, which has the following procedure:

  1. Shut down your computer.
  2. Disconnect all Thunderbolt and USB storage devices, except for the USB media which contains the Windows ISO installer.
  3. Try the installation again.

But the reason we had any USB drives plugged in was because we had thought Boot Camp Assistant was going to store the Windows installer on that flash drive. So why was Windows complaining?

The answer is Boot Camp in El Capitan does not store the Windows ISO installer on a USB flash drive. Instead, the Boot Camp Assistant will create a temporary FAT32 partition, name it OSXRESERVED, and store the Windows installation files on the OSXRESERVED partition.


Since the USB flash drive wasn’t being used as the source of Windows installer files, having it plugged in was causing the error to appear.

So we shut down, unplugged the USB flash drive, and again re-ran the installation. This time, no error and Windows 10 installed without a problem.

Plain desktop windows 10 screenshot 03 18 15 2

  1. September 2, 2016 at 6:54 pm

    It also really doesn’t like operating on Macs that’ve been Filevault 2’d as well. So all this, bootcamp THEN enable FV2 or you’ll get to this same screen and fail.

  2. Larry S
    September 8, 2016 at 8:53 pm

    hey Rich
    just did this today using an external USB 3.0 Drive, left the drive plugged in, performed the same steps and had no issues. Could this be hardware specific? I was working on a mid 2013 13″ Macbook Air (K-12)

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