I am happily running Catalina (on a Macbook Air 2017) and am tempted to upgrade to BigSur, but I'm a little leery of breaking apps, particularly Arduino IDE (which appears problematic, from the little searching I've done). So I want to make the system dual-boot - my existing Catalina installation, and BigSur (or perhaps Monterey) - and live with the new OS for awhile before I commit.
There are numerous articles describing the process, in brief: use Disk Utility to add a new volume, download the appropriate installer, and install the new OS on the new volume. But beyond that ?
It seems there are two ways to go:
Use Migration Assistant to import everything (apps, home folders, other files) to the new BigSur volume, thus two completely independent systems.
Use SystemPrefs -> Users&Groups "advanced" to point the home folder (when logged into BigSur) to the Catalina volume.
It seems each path has advantages and disadvantages and I'm not sure which to do. #1 has the disadvantage that there's two copies of user data, thus the issue of keeping in sync - probably best achieved by only modifying files in one. But #2 has the disadvantage that certain files (e.g. ~user/Library) may need to be different for the new OS (I'm pretty sure that's the case for Arduino IDE).
How should I slice this cake ?
As requested below, here is the current state of my disk:
% diskutil list internal
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *240.0 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS Container disk1 239.8 GB disk0s2
/dev/disk1 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +239.8 GB disk1
Physical Store disk0s2
1: APFS Volume MacHD - Data 88.3 GB disk1s1
2: APFS Volume Preboot 91.1 MB disk1s2
3: APFS Volume Recovery 529.0 MB disk1s3
4: APFS Volume VM 4.3 GB disk1s4
5: APFS Volume MacHD 11.2 GB disk1s5
After installing Big Sur ...
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *240.0 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS Container disk1 120.0 GB disk0s2
3: Apple_APFS Container disk2 119.8 GB disk0s3
/dev/disk1 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +120.0 GB disk1
Physical Store disk0s2
1: APFS Volume MacHD - Data 84.9 GB disk1s1
2: APFS Volume Preboot 91.1 MB disk1s2
3: APFS Volume Recovery 529.0 MB disk1s3
4: APFS Volume VM 1.1 GB disk1s4
5: APFS Volume MacHD 11.2 GB disk1s5
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +119.8 GB disk2
Physical Store disk0s3
1: APFS Volume BigSur 67.3 GB disk2s1
2: APFS Volume Preboot 287.6 MB disk2s2
3: APFS Volume Recovery 625.7 MB disk2s3
4: APFS Volume VM 1.1 MB disk2s4
5: APFS Volume Big Sur 15.3 GB disk2s5
6: APFS Snapshot com.apple.os.update-... 15.3 GB disk2s5s1
