Installing Mojave on New Volume from Catalina

[JDSPGA]

Hi,

My wife is currently devastated that most of her favorite steam games don't work with 64 bit Catalina. The "easy" fix seems to be to create a new disk volume and install Mojave, and then boot into that. She doesn't want to revert the entire system back as she needs work related stuff to remain intact on her current OS/disk.

It seems like installing a new OS on a new volume is easy when installing a beta of a future version of an OS, but it's proving difficult to do when trying to install Mojave on a volume while currently running Catalina, as the installer downloaded from the app store won't open as the OS doesn't support it.

What is the solution here?

Thanks!

 

[posguy99]

Make a USB installer, create another volume in the existing container, and install.

 

[Taz Mangus]

I would suggest creating a new partition for the Mohave install. I would not suggest creating a new Volume in the same Catalina Container. Create the new partition Container from the bootable Mojave installer.

 

[JDSPGA]

I would suggest creating a new partition for the Mohave install. I would not suggest creating a new Volume in the same Catalina Container. Create the new partition Container from the bootable Mojave installer.

That was my initial instinct. The issue is she only has like 12 gigs of free space. Might need to free some space up.

What is the disadvantage of just creating the volume?

Thank you for the advice both of you.

 

[Taz Mangus]

That was my initial instinct. The issue is she only has like 12 gigs of free space. Might need to free some space up.

What is the disadvantage of just creating the volume?

Thank you for the advice both of you.

Catalina introduce some new features in APFS in Catalina and it could be an issue booting or installing Mojave in a Catalina created container.

Keep Catalina and Mojave separate from each other.

 

[chrfr]

Catalina introduce some new features in APFS in Catalina and it could be an issue booting or installing Mojave in a Catalina created container.

Keep Catalina and Mojave separate from each other.

There are issues with putting Big Sur and earlier OSes on separate volumes, but my experience is that Mojave and Catalina can coexist without problems.
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That was my initial instinct. The issue is she only has like 12 gigs of free space. Might need to free some space up.

With only 12GB free, you won’t be able to install to a new volume either- it won’t have enough space available. Maybe an external SSD would be a better option for your Mojave disk.

 

[Taz Mangus]

There are issues with putting Big Sur and earlier OSes on separate volumes, but my experience is that Mojave and Catalina can coexist without problems.

Good point. I guess I was thinking about Big Sur APFS changes.

 

[HDFan]

The issue is she only has like 12 gigs of free space.

In addition to the space for the install, you need to keep 20-30% of your disks free to avoid performance and reliability issues.

 

[haralds]

That was my initial instinct. The issue is she only has like 12 gigs of free space. Might need to free some space up.

What is the disadvantage of just creating the volume?

Thank you for the advice both of you.

I have used new Volumes in the same container without trouble. The advantage is volumes in the same container all share free space. They are also easily deleted.
My MacBook Pro has High Sierra, Mojave, Catalina, and Birg Sur in one container. One should note that it is not yet recommended to install Big Sur into a volume shared with Catalina or Mojave.
12GB is not enough. I have Mojave for games and it is at 123GB at this point. I would recommend at least 30GB for the OS plus whatever space you need for games. macOS is not graceful when it runs out of space.