There was a thread in the High Sierra forum where the OP asked about partitioning a disk for using High Sierra and the Mojave beta.
https://forums.macrumors.com/threads/partioning-high-sierra-with-another-drive.2122360/
In that thread, I was wondering whether High Sierra and Mojave could be put in the same APFS container. I looked in this forum but couldn't find anything (sorry if I missed it in the 100+ threads that were there at the time). I looked in the Apple developer forums. I searched the web. The only thing I could find was an article in Italian.
So I decided to try it out (wasn't planning on using the Mojave beta previously). It turns out that you can put High Sierra and Mojave in the same APFS container and it turns out to be pretty trivial - maybe that's why there isn't much on this.
To do this, you obviously have to have free space in your APFS container.
Start the Disk Utility app.
- Select the APFS container where you want Mojave. In my case, that was "Container disk2", which is selected above.
- Either right-click and select "Add APFS Volumes" or from the top Disk Utility menu, select Edit -> Add APFS Volume.
- The dialog box "Add APFS volume to container?" will appear. In my case, I set a starting size of 40GB in "Size Options".
- Press the "Add" button.
(The "Mojave" volume already appears because the screenshot was taken after the Mojave installation.)
In the Mojave installation app, in the beta at least, only my existing High Sierra "rd400" appeared as the target volume. Press "Show All Disks..." and the new volume should appear.
When the installation is done, the Mojave volume should appear as an option in the Startup Manager (Option/Alt key at boot) and in the list of startup volumes in System Preferences.
The following is what diskutil list showed for the container before (in High Sierra) and after the Mojave installation. Notice there is only one Preboot and one Recovery volume. I don't think that the doubling in size of the Recovery and Preboot volumes is important - the other SSD in the computer which only has High Sierra on it has volume sizes which are about the same size and those sizes did not change because of the Mojave install.
I tested going into recovery mode. I was not given a choice of which recovery to go into even though I had High Sierra and Mojave on one SSD and High Sierra on the other. In recovery mode, I was poking around and in exiting MacOS Utilities, it froze at a grey screen so maybe it was Mojave recovery - I don't know.
Obviously the big advantage of putting High Sierra and Mojave in the same APFS container is that you don't have to do the old-style re-partition or worry about whether the size you're assigning to the volumes is going to be correct. Once you're done with the Mojave beta, zap the volume and it will be available to the other volumes. Or, upgrade the Mojave beta to release, migrate and then zap the High Sierra container.
The caution will need to be given - if the APFS container code proves unreliable, that could have catastrophic results for both High Sierra and Mojave volumes so proceed at your own risk. I installed Mojave on a SSD I'm using for testing purposes.
https://forums.macrumors.com/threads/partioning-high-sierra-with-another-drive.2122360/
In that thread, I was wondering whether High Sierra and Mojave could be put in the same APFS container. I looked in this forum but couldn't find anything (sorry if I missed it in the 100+ threads that were there at the time). I looked in the Apple developer forums. I searched the web. The only thing I could find was an article in Italian.
So I decided to try it out (wasn't planning on using the Mojave beta previously). It turns out that you can put High Sierra and Mojave in the same APFS container and it turns out to be pretty trivial - maybe that's why there isn't much on this.
To do this, you obviously have to have free space in your APFS container.
Start the Disk Utility app.
- Select the APFS container where you want Mojave. In my case, that was "Container disk2", which is selected above.
- Either right-click and select "Add APFS Volumes" or from the top Disk Utility menu, select Edit -> Add APFS Volume.
- The dialog box "Add APFS volume to container?" will appear. In my case, I set a starting size of 40GB in "Size Options".
- Press the "Add" button.
(The "Mojave" volume already appears because the screenshot was taken after the Mojave installation.)
In the Mojave installation app, in the beta at least, only my existing High Sierra "rd400" appeared as the target volume. Press "Show All Disks..." and the new volume should appear.
When the installation is done, the Mojave volume should appear as an option in the Startup Manager (Option/Alt key at boot) and in the list of startup volumes in System Preferences.
The following is what diskutil list showed for the container before (in High Sierra) and after the Mojave installation. Notice there is only one Preboot and one Recovery volume. I don't think that the doubling in size of the Recovery and Preboot volumes is important - the other SSD in the computer which only has High Sierra on it has volume sizes which are about the same size and those sizes did not change because of the Mojave install.
Code:
High Sierra
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +255.9 GB disk2
Physical Store disk1s2
1: APFS Volume rd400 96.2 GB disk2s1
2: APFS Volume Preboot 21.5 MB disk2s2
3: APFS Volume Recovery 518.1 MB disk2s3
4: APFS Volume VM 3.2 GB disk2s4
Mojave
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +255.9 GB disk2
Physical Store disk0s2
1: APFS Volume rd400 102.7 GB disk2s1
2: APFS Volume Preboot 44.6 MB disk2s2
3: APFS Volume Recovery 1.0 GB disk2s3
4: APFS Volume VM 2.1 GB disk2s4
5: APFS Volume Mojave 40.0 GB disk2s5
I tested going into recovery mode. I was not given a choice of which recovery to go into even though I had High Sierra and Mojave on one SSD and High Sierra on the other. In recovery mode, I was poking around and in exiting MacOS Utilities, it froze at a grey screen so maybe it was Mojave recovery - I don't know.
Obviously the big advantage of putting High Sierra and Mojave in the same APFS container is that you don't have to do the old-style re-partition or worry about whether the size you're assigning to the volumes is going to be correct. Once you're done with the Mojave beta, zap the volume and it will be available to the other volumes. Or, upgrade the Mojave beta to release, migrate and then zap the High Sierra container.
The caution will need to be given - if the APFS container code proves unreliable, that could have catastrophic results for both High Sierra and Mojave volumes so proceed at your own risk. I installed Mojave on a SSD I'm using for testing purposes.
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