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First time poster here.

After installing High Sierra on my iMac (27", late 2012) my Boot Camp Windows 10 partition is no longer visible in the Startup Manager (accessed by holding Option-key on startup).

When logged into Mac OS, I can see the bootcamp-disk, and it's also visible in Startup Disk. Edit: it's visible in Finder, hence a different problem than described in other questions.

Edit: When I try to boot to Win from Startup Disk, the computer froze on first attempt. On second attempt, it displayed "no bootable device - insert disk and press any key".

I run OS X 10.13.2. Any help is greatly appreciated, thanks in advance! /Johan

Edit: the disk is a "fusion drive".

Edit: As a (at least temporary) solution, would it be possible to roll back the system using Time Machine, to before the High Sierra uppgrade?

Edit: I solved the issue by simply removing the bootcamp partition, starting from scratch with a new Win 10 installation. However, the Win installation failed several times. The installer wouldn't accept the bootcamp partition. After some googling I did a PRAM-reset, which did the trick. I don't know if this was caused by my original problem with the missing partition.

Thanks for the replies and suggestions, guys!

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I do not yet have enough information to diagnose your problem. However, I can offer an solution to one possible scenario that fits what you have posted.

I assume you started with a previous version of Windows, say Windows 7. At some point you upgraded to Windows 10. If this is true, the you would have been using the legacy BIOS boot method, which requires a hybrid GPT/MBR partitioning scheme.

It is possible the macOS upgrade converted a Hybrid partition scheme back to a pure GPT scheme. In this case, you problem is a duplicate of How to convert a drive from the GPT format to the hybrid GPT/MBR format when using High Sierra (macOS 10.13.2).

Before implementing any solution, I would start by determining whether your Mac is trying to boot Windows using the legacy BIOS or the newer EFI boot method.

This can be done by executing the following steps.

  1. Open "Startup Disk" under "System Preferences".
  2. Unlock if necessary.
  3. Select the icon labeled Windows. Do not restart the computer.
  4. Quit "System Preferences"
  5. Open a Terminal application window.
  6. Enter the command given below.

    bless  --info  --getBoot  --verbose  2>&1  |  grep  -i  legacy
    
  7. If you are using a legacy BIOS boot method, then the output should appear similar to what is shown below.

    Legacy mode suppported
    Boot option is a legacy device
    Searching for legacy type 'HD'
    Legacy mode suppported
    Legacy mode suppported
    Matching legacy device 'disk0s4'
    Legacy boot device detected
    

    If you are using the newer EFI boot method, then the command will produce no output.

  8. Repeat steps 1 through 4, except select icon with label indicating the volume you have currently booted from.

If you post the output from the the command shown in step 6, I can update my answer with a better explanation on how to proceed.

Also, the output, from the command given below, can help diagnose your problem.

diskutil  list
  • Thank you! However, the Win 10 installation is the first windows installation I've made on this computer. No other versions have been installed, no upgrade has been made. I decided to simply remove the bootcamp partition and reinstall it. However, this seems to have given me new problems, which may or may not be related to this question. I'll get back. – Signert Dec 17 '17 at 9:39
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Yes - you certainly can roll back with a bootable installer.

You could make two (or more partitions) on an external drive and run the createinstallmedia and have a Sierra installer, High Sierra installer and boot to either - erase your drive (disconnect all backup drives so you’re sure you don’t erase your backup) and then install Sierra.

When the setup assistant runs - try restoring your latest backup - in general that’s not supported, but I’ve had luck with it on Sierra/HS upgrades lately. If you want to be 100% safe and supported, choose a backup from Sierra to restore to Sierra, though.

  • I didn't do this, as you can see in my edit, but it's very useful advice. I'll save it. :) – Signert Dec 18 '17 at 20:28

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