APFS and HFS+

[CooperBox]

I wish to install OS Mojave (or possibly Catalina) and OS Sierra onto a new SSD, to be installed in a mid 2012 13" MacBook Pro.
I'm aware that Mojave will format a partition as APFS, and until now I've run Sierra on a HD formatted as Mac OS Extended (HFS+).
My question is simple: can I format the new SSD with 2 partions, APFS and Mac OS Extended? If so are there any diffculties I'm likely to encounter? Should Mojave (or Catalina) be installed first, then Sierra or doesn't it matter?
Thanks.

 

[casperes1996]

You can partition it up just fine though of course with the traditional partitioning methods and not APFS volume sharing containers since that would only allow several APFS volumes. This means you need to decide the size of each partition in advance - APFS only systems can dynamically grow their volumes in a space sharing container.

The order doesn't really matter since the two partitions should act as isolated systems anyway, but when formatting the drive I would personally do it from the newer OS, since that allows you to create the APFS and HFS+ partitioning from the beginning with the latest APFS revision, so for that reason I'd start with the newer OS, but it's not strictly speaking necessary

 

[Fishrrman]

My suggestion:
(I actually did this with the internal drive on my 2018 Mini)

You need a way to connect the SSD to the Mac "externally".
It could be a 2.5" enclosure or perhaps a USB3/SATA adapter dongle, or a USB3/SATA docking station. Then...

- erase the drive (initialize it) using disk utility. Use "Mac OS extended with journaling enabled, GUID partition format" (HFS+).

- now, PARTITION the drive into two partitions (both will still be HFS+). "The first one" will be used for Mojave, the second for High Sierra (see next step)

- once the partitioning is complete, with disk utility still open, select the first partition. I believe there's an option in disk utility to "convert to APFS". Run this on the first partition, leave the second one HFS+.

Now you have a drive partitioned "two ways" -- APFS on the first, and HFS+ on the second.
From this point you can clone over your OS's, re-install them, your choice.

Final thoughts:
I believe Mojave will run just fine in HFS+, with ONE EXCEPTION:
Software Update will not work on Mojave running under HFS+.
When I was first setting up the Mini I'm using today, I "cloned over" Mojave from an external drive to the Mini's internal drive, and it booted and ran ok. But that's when I found Software Update no longer functioned properly. So... I erased the boot partition, then "converted it to APFS" (as detailed above), RE-cloned Mojave back to it, and now Software Update works as intended.

 

[CooperBox]

Thanks for the feedback guys. Very useful.