Dual boot Mojave and High Sierra: 2018 MBP

[anshuvorty]

Hi,

I have read about the horror stories that people have had when they have wiped their 2018 MBP and went ahead and tried to reinstall High Sierra that their machines have ended up in boot loops and the only solution was to replace the machine (something to do with the T2 chip and not being able to communicate with the Intel CPU because of encryption).

I am thinking about dual booting Mojave and High Sierra and since this is my 1st time going through this process, I would like some help.

Notably, while searching for this online, I came across advice that I would need to format my hard drive, then create 2 partitions. On one partition, to reload my High Sierra install through a Time Machine backup, and on the other, to do the same (reload High Sierra) and then install Mojave.

Since I am apprehensive of going through the format and reinstall process, is there an easier way to dual boot these two OSs?

I am not looking into virtualization as on the MBP, with its low core count, the experience will be miserable.

Thanks!

 

[campyguy]

On a iMP, figured I'd chime in. Dual boot with HS and Mojave, zero issues with the install and maintenance.

One recommendation, with Disk Utility do not create a "partition" for Mojave - create a Volume. There is a difference, no need to rewrite the partition table with a Volume.

My process was simple. With Disk Utility, created a Volume named "Mojave" and formatted it was APFS. DLed the Mojave installer and ran it, choosing the install to be placed in the "Mojave" Volume - the installer worked without issue. After the Mojave install, I updated it (I waited until DP4). No issues, I generally boot into HS and use the Option Key to select the Mojave Volume. QED, again, zero issues.

If you do opt for the install, be prepared for the newfound zippiness from the boot time to, well, pretty much everything else...

 

[thebitguru]

I blogged about the volume option that campyguy mentioned and would recommend it too. Check this out: https://thebitguru.com/blog/1499-ho...ave-without-messing-with-your-primary-install

 

[anshuvorty]

On a iMP, figured I'd chime in. Dual boot with HS and Mojave, zero issues with the install and maintenance.

One recommendation, with Disk Utility do not create a "partition" for Mojave - create a Volume. There is a difference, no need to rewrite the partition table with a Volume.

My process was simple. With Disk Utility, created a Volume named "Mojave" and formatted it was APFS. DLed the Mojave installer and ran it, choosing the install to be placed in the "Mojave" Volume - the installer worked without issue. After the Mojave install, I updated it (I waited until DP4). No issues, I generally boot into HS and use the Option Key to select the Mojave Volume. QED, again, zero issues.

If you do opt for the install, be prepared for the newfound zippiness from the boot time to, well, pretty much everything else...

I blogged about the volume option that campyguy mentioned and would recommend it too. Check this out: https://thebitguru.com/blog/1499-ho...ave-without-messing-with-your-primary-install

Thanks for these tips. I have now been able to install the Public beta on the separate "Volume" and it is running fine. I did specify the Reserve Size in the Size Options window in Disk Utility as 60 or so GB (I can't remember), however, Disk Utility is showing the Mojave "volume" as having 182 or so GB free. Shouldn't it say < 60 GB free?

What is going on?

 

[thebitguru]

It "reserved" 60GB (minimum size), but the volume can grow more than that unless you also specified the "Quota Size" (maximum size) when creating the volume.

 

[campyguy]

What is going on?

Long day, just a few minutes here today. Agreed with the above answer. Container Volumes dynamically adjust in size. My "Mojave" Volume was showing as "1GB" in size before the install, now around 83GB in size with the OS and a few apps (Logic Pro X, GarageBand 6 and 10, Pages - I can't live without GB 6's Magic GarageBand!) installed.

Add stuff, the Volume increases in size. Delete stuff, the Volume decreases in size. No need to futz with partition maps now. FWIW, I was hung up on partitions from my own experience, took the leap after reading up on the principle. There's beauty in Container Volumes, I'm finding... I'm so over partitioning on the macOS platform now.

 

[dsemf]

I also use the Mojave volume approach. When I first started Mojave after the initial install it asked if I wanted to mount the encrypted Macintosh HD volume with High Sierra. I supplied the HS password and I had full access. I use that to selectively copy data to Mojave volume for testing.

It would be really neat if Apple came up with way to make it possible to install Windows or Linux in an APFS volume that was bootable.

DS

 

[coolbreeze2]

I blogged about the volume option that campyguy mentioned and would recommend it too. Check this out: https://thebitguru.com/blog/1499-ho...ave-without-messing-with-your-primary-install

I am going to try this method to install dual boot on an iMac.