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Guide: Multibooting UEFI on Separate Drives

Is there a significant benefit to using UEFI boot? I mean how many of us are using >2TB boot volumes?

I am still a fairly huge fan of "Legacy" boot because then you can boot directly off the MBR by simply aiming your BIOS to boot from that specific drive. Seems a lot safer than screwing around with various bootloaders only to have it nuked when you do an update? I had rEFInd installed on my MBP for enabling external thunderbolt eGPU in Windows but when I upgraded to Mojave, it was wiped out and the original OS X bootcamp bootloader was re-installed (this is on my 2018 MBP)
 
Is there a significant benefit to using UEFI boot?
Yes, many more benefits than just having a >2TB volume.

For Hackintoshers booting Clover UEFI it opens up all the potential functions in Clover like UEFI hot patching.

In more general terms for PCs here are the main ones.

Benefits of UEFI boot mode over Legacy BIOS boot mode include:

1) Support for hard drive partitions larger than 2 Terabytes

2) Support for more than four partitions on a drive

3) Fast booting and efficient power and system management

4) Robust reliability and fault management
 
For Win10:
[...]Reboot to BIOS/UEFI and disable CSM. Save&exit, continue boot to desktop. Shut down, disconnect the drive.

Thanks for the guide. I have Mojave running fine on a Hackintosh. Until now, Mojave has been the only OS on the machine. I want to add Windows 10 on a separate drive. I have followed your guide. The last step in your Win10 instructions - disabling CSM - is where I first run into trouble: CSM support is set to "ALWAYS" and greyed out in the BIOS/UEFI-interface, so I can't change its setting. (?)

More importantly, when both drives (Mojave and Win10) are connected, the machine will only start up in Windows. Clover is never initiated. If I disconnect the Win10 drive, Clover and Mojave start up as usual.

Any suggestions?
 
Thanks for the guide. I have Mojave running fine on a Hackintosh. Until now, Mojave has been the only OS on the machine. I want to add Windows 10 on a separate drive. I have followed your guide. The last step in your Win10 instructions - disabling CSM - is where I first run into trouble: CSM support is set to "ALWAYS" and greyed out in the BIOS/UEFI-interface, so I can't change its setting. (?)

More importantly, when both drives (Mojave and Win10) are connected, the machine will only start up in Windows. Clover is never initiated. If I disconnect the Win10 drive, Clover and Mojave start up as usual.

Any suggestions?
With both drives connected boot to UEFI/BIOS. Set the Mac OS drive as first in BBS boot order. Save&exit, continue boot. It should boot to Clover and allow you to choose OS to boot.
 
With both drives connected boot to UEFI/BIOS. Set the Mac OS drive as first in BBS boot order. Save&exit, continue boot. It should boot to Clover and allow you to choose OS to boot.

Thank you very much! I didn't really find anything called "BBS boot order" in the UEFI/BIOS, but I did find some drive icons that seemed to be listed in a certain order. I tried dragging them around and found that I could change the order of them that way. This helped! Now the machine automatically runs Clover at startup - and I can see a couple of drives with a Windows icon in Clover.

However, when I choose the Windows drive that says EFI on it in Clover, Windows freezes at startup. If, however, I press F12 at startup and manually choose the correct Windows startup volume in the UEFI/BIOS (before Clover is initiated), Windows starts up just fine. Also, I notice that Clover is annoyingly slow at startup (reporting that it is checking hardware etc.). My son (it's my son's computer) says it been that way for a while (before we installed Windows) - slow, but maybe not THAT slow.

I am unsure of the correct etiquette here. Perhaps I should start a new thread about those problems?
 
Thank you very much! I didn't really find anything called "BBS boot order" in the UEFI/BIOS, but I did find some drive icons that seemed to be listed in a certain order. I tried dragging them around and found that I could change the order of them that way. This helped! Now the machine automatically runs Clover at startup - and I can see a couple of drives with a Windows icon in Clover.

However, when I choose the Windows drive that says EFI on it in Clover, Windows freezes at startup. If, however, I press F12 at startup and manually choose the correct Windows startup volume in the UEFI/BIOS (before Clover is initiated), Windows starts up just fine. Also, I notice that Clover is annoyingly slow at startup (reporting that it is checking hardware etc.). My son (it's my son's computer) says it been that way for a while (before we installed Windows) - slow, but maybe not THAT slow.

I am unsure of the correct etiquette here. Perhaps I should start a new thread about those problems?
The correct Win10 icon is labeled Boot Windows EFI from EFI.
 
So, Question (it's actually in the next para. - this is background): In order to create my Windows installer USB booter, I had to use Bootcamp in MacOS Mojave: I created a bootcamp Windows installation on my second (Windoze) SSD. When it was installed, from within that windows I created my PROPER Windows installer USB. Then, I formatted the main bootcamp windows permission but left the existing UEFI/EFFI (not sure what you call it). Everything seems fine. I think.

MY QUESTION IS.... is there any lingering screwy-ness from that bootcamp "efi" partition or whatever, and is that possibly affecting my Clover EFI installer -- maybe screwing up my windows somehow and not enabling certain hardware I'm not aware of, etc.? Everything seems pretty great ? I just want to make sure because.. .I have .. no idea.
 
MY QUESTION IS.... is there any lingering screwy-ness from that bootcamp "efi" partition or whatever, and is that possibly affecting my Clover EFI installer -- maybe screwing up my windows somehow and not enabling certain hardware I'm not aware of, etc.? Everything seems pretty great ? I just want to make sure because.. .I have .. no idea.
Should not be. The only difference when you installed using bootcamp is that is placed the UEFI partition at the beginning of the drive. Windows usually installs the UEFI either second or third position and Clover does not like it there. You should have no problems.
 
Shut down, disconnect the drive.

I already have Windows and macOS installed on separate SSDs on an existing installation and everything is running smooth. I already have a 3rd SSD in the same tower I'd like to install a Linux distro on. Since everything is all buttoned up and to save me a little time, is it necessary to disconnect the Windows SSD before proceeding with the Linux installation?
 
I already have Windows and macOS installed on separate SSDs on an existing installation and everything is running smooth. I already have a 3rd SSD in the same tower I'd like to install a Linux distro on. Since everything is all buttoned up and to save me a little time, is it necessary to disconnect the Windows SSD before proceeding with the Linux installation?
No. As long as you are able to distinguish which drive is which there is no need. Disconnecting the other drives is a precaution to prevent mistakenly overwriting one OS over another. With the newer UEFI of most new boards you can bot to UEFI and simply disable the ports, eliminating the need to physically disconnect the drives (provided you can determine which drive is on which port).
 
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