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Guide: MultiBoot Success with Mojave/Win10 on 2 internal SSDs and ASUS mobo

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Aug 30, 2016
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Motherboard
Asus MAXIMUS XI HERO
CPU
i7-8700K
Graphics
RX5700 XT
Mac
  1. iMac
Classic Mac
  1. iMac
Mobile Phone
  1. Android
My correct recipe for this setup got buried in a long whiny thread (me whining, that is). I thought it was useful enough -- and I've multibooted enough times and run enough stuff on both OS with no problems -- that I'm reposting it here with its own title and calling it Success.

2 internal SSDs. Mojave is on the M.2 NVME SSD on the mobo. The Win10 target is an SSD in a PCIe adapter in slot 3. ASUS MAXIMUS XI HERO. SSDs cannot be disabled in ASUS BIOS. And it's a PITA to remove the one mounted right on the mobo which is where Mojave is installed. So the Mojave SSD (which was installed first) will inevitably get clobbered when Win10 installs.

Therefore:

BEFORE YOU TOUCH WIN10 MEDIA (and get cooties):
On the MacOS side, do this:

If I had only done this first, I would have saved myself about three days of hair tearing and cussing. I used the UEFI Shell method.

Oh yes, of course make sure Clover is option #1 on your boot menu also.

Now your Clover is safe from Win10 stomping and you won't get into a scary catch-22 situation like I did. Now you can don your biohazard clothing and get into the Win10 stuff.

Step 0: Use Rufus to make a Win10 USB install stick (see note below)
Step 1: Disable SATA in ASUS BIOS so Win10 doesn't go scribbling boot loaders on your data disks
Step 2: Boot your Rufus stick, using UEFI Boot Menu (F8 key on my mobo)
Step 3: Get Windows Installer start screen
Step 4: Shift-F10 to get command shell
Step 5: Use diskpart to clean target disk, just to be sure
Step 6: Exit to installer
Step 7: Go through activation code blah blah, get to disk menu
Step 8: Choose the disk (should be obvious because it has no partitions any more)
Step 9: (for me this was important) Press New button, don't try to install directly into Unallocated Space
Step 10: Disk gets partitioned with MBR and primary, but don't panic... don't reformat, don't manually add EFI!
Step 11: Now select Primary partition and Install
Step 12: Win10 install screen with progress bar. This is where it goes sideways if you've made an error.
Step 13: Assuming you made no errors, install continues with another boot. Not the stick this time, remove it.
Steo 14: And here the magic begins: at this point I was able to boot Win10 from Clover woo-hoo!
Step 14: Finish WinDoze setup, install driver for your GPU, disable auto updates, remove bloatware, customise, whatever.
Step 15: Restart.
Step 16: Get back into BIOS. Turn SATA back on. Verify Clover is #1 boot option.
Step 17: If this works for you as it just did for me, you should now be able to boot into Win10 or Mojave from Clover. Repeatably.

So out of all the clever tricks from all the clever people who so generously help eejits like me, the one that really changed the game was using the UEFI Shell in Clover to make a hard coded boot entry for Clover, so that Win10 stomping the "Windows Boot Manager" no longer breaks anything. It can stomp all it wants.

About that Rufus boot stick: this seems like a chicken/egg problem and it is: without a Win10 machine you can't make the stick. I run Parallels VM on my Hackie and have for 3 years. It turns out that the through-access to USB devices is good enough to allow Win10 VM to format and write a USB stick, so I just ran Rufus in the VM and made my boot medium. If you didn't have a WinDoze machine (even virtual) then I guess you'd have to write the ISO to a DVD and try booting it from your optical drive (if you had one).
 
First off: Thank you very much OP!

Step 1: Disable SATA in ASUS BIOS so Win10 doesn't go scribbling boot loaders on your data disks

I guess you are talking about disabling the respective sata ports with MacOS installed?
(thats why it would work from an optical drive I guess? - that would be my approach since I have no Win10 PC at my disposal)

Edit; Second question: As I read it, its not critical to put the win install on the first sata port?

Thx!
 
Last edited:
Yes, sorry, when I said to disable SATA, that was because I was working with two SSD's and so SATA drives were not involved and could be safely kept out of the picture. If you need your optical drive to load the DVD with the Win10 ISO in it then obviously that SATA unit must be enabled :)

In my ASUS BIOS I can disable all SATA devices with just one click, or I can disable selectively one unit at a time. I disabled them all at once because it was easier.

I didn't install Win10 on any SATA device, so I don't know how it would respond to being installed on SATA units other than the first port... In my SSD set up, Win10 thought that the PCIe SSD it was installing on was "Drive 0" and the M.2 NVME SSD (on the mobo) was "Drive 1" so perhaps that helped in keeping it happy.

Do note that though disabling a SATA boot drive with MacOS on it does protect it from the bootloader stomp during your initial Win10 install from optical media or thumbdrive, it will not be protected later from Win10 system upgrades which may spontaneously stomp it. So that initial step of creating the hard-coded UEFI boot record for Clover is still important, no matter which type of drive you end up installing Win10 on. At least that's how I understand things.
 
BIG thanks!
My (appearantly successful) procedure:

0. Complete backup
1. Create the hard-coded UEFI boot record with only my mac drives connected
2. Create Win10 Thumbdrive with rufus
3. Disconnect Mac NVMe (second port) and all the data drives, then put in my to-be windows nvme (first port)
4. install windows + drivers install (graphics, Wifi, BT, FW-Card), deactivate automatic updates (I dont know if thats necessary though with the hard-coded boot entry?)
5. Shut down and reconnect the Mac NVMe
6. Restart and correct boot order
7. Checked if everything is fine, then connected my data drives
8. :thumbup: everything okay after 7 restarts now

Thank you very very much, your posting + guide were perfectly in time for me!

Problems I encountered:
My Saffire Pro40 FW Soundcard on a Syba FW Card would freak out at first connecting and disconnecting like crazy, however when I installed the win legacy driver, at first nothing changed but at the third restart, everything worked all of a sudden (windoze automatically sets it to 96k/24bit).

What I would do differently:

When creating the Win partition in the installer I didn't give it a name, so showing up in MacOs its now called "untitled"...
I don't really care - however: I'd like to hide the Win Partition in MacOS anyways (would you know how to do that?)

Questions I came across while creating the boot-entry:

When listing the drives in the UEFI-Shell my NVMe appeared 4 times in the list which made it kind of hard at first to identify the right drives until I figured out how to identify the UEFI Partition... Any experts on why that my be the case?
 
Congratulations! Glad to hear you succeeded. For whatever reason, I'm not seeing my Win10 partition mounting when I log in to Mojave. That's probably a Good Thing. Even though I have NTFS support under Mojave I don't really trust it with a bootable disk :) I do recollect that at times the Win10 partition has automounted on Mojave -- like you I could see a volume called "untitled" -- but I don't know when or why it stopped doing that.
 
Congratulations! Glad to hear you succeeded. For whatever reason, I'm not seeing my Win10 partition mounting when I log in to Mojave. That's probably a Good Thing. Even though I have NTFS support under Mojave I don't really trust it with a bootable disk :) I do recollect that at times the Win10 partition has automounted on Mojave -- like you I could see a volume called "untitled" -- but I don't know when or why it stopped doing that.
If you want something other than "untitled", boot Win10, open a Windows explorer window, right click on the C drive and select properties. Type a name in the box and click apply/save.
 
thx for your feedback + help!

I've now come across another "problem" that might in some sort be related to this guide.

I created that hard-coded boot entry for clover (now on latest=5103) - but now, after updating my EFI to emuvariables + quirks + quirks.plist I realized that I forgot to copy FW runtimeservices.efi.

Bildschirmfoto 2020-02-02 um 23.33.31.png

But it still works?

So my mac seems to be running without a memory driver (which should be impossibruuu).

So could it be that by making that boot entry I created some kind of extra EFI folder (that is not visible to any efi-mounting software I am aware of)

??

Anybody got a clou what I am missing?

Thx!
 
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