How to convert to APFS non-destructively?

Unfortunately, the only way to convert HFS+ to APFS, non-destructively, is when you install Catalina from the upgrade installer application. Apple has the procedure but have not made that public. It's locked in the Install macOS Catalina application. I'm afraid that you have no way to make the switch, non-destructively, unless you download the Catalina installer and upgrade your system with it.

The only way to convert non-destructively is if the drive is empty. Otherwise, you must reformat the drive. HFS+ and APFS are very different, so the conversion from one to the other is not that simple.

I would suggest the following outline:

1. Boot from the Recovery Volume.
2. Open Disk Utility and run First Aid on the startup volume.
3. Clone the startup volume to an external drive that is exactly the same size as the startup volume or larger.
4. Restart the computer using Option boot and select the external clone as the startup volume.
5. Open Disk Utility on the startup volume and reformat the old startup volume using APFS.
6. Clone the external startup volume back to the old startup volume using Disk Utility.

Note: The size of the volumes as used above means they each have an equal number of blocks. Do not rely on indicated sizes in GBs as two drives may be advertised as the same in GBs but may differ in the number of blocks. Disk Utility will not clone a drive that is even one byte larger than the target drive.

If it didn't convert when you installed Mojave, there is likely a reason, and that reason is probably also preventing you from converting.

I don't know what would cause that, but I imagine the only way to resolve it is to back up, erase the drive, install the OS, then migrate from the backup.

David King1 wrote:

I noticed that my iMac internal drive is macOS Extended (Journaled). When I upgraded from High Sierra to Mojave I guess the conversion to APFS didn't take place.

I'm looking for ways to convert to APFS - I followed the instructions in the Mac Observer site but that doesn't work.

I'm able to boot with the Recovery Drive but when I go to Disk Utility and try and Convert the internal drive, the option (Convert) is greyed out ... i.e. not available to me.

Is there a way to convert my drive to APFS without having to reformat the internal drive?

iMac late 2015, Mojave 10.14.6, 24GB RAM, 4TB internal hard drive.

Thanks.

Convert to APFS option not available or greyed out

https://developer.apple.com/forums/thread/84692

Reluctant to go to Catalina just yet ... I've heard that Disk Warrior is not ready for Catalina. Without DW I'll be up the creek without a paddle if my drive acts up ...

In 30+ years, I have never had a drive "act up." I have never needed anything but Disk Utility.

I have had a few drives fail, but never anything else.

About Disk Warrior: From the Alsoft website. DW doesn't rebuild any APFS formatted disks. I long ago gave up on DW. It has fallen way behind. They have been promising the upgrade for APFS for several years. Nothing has happened.

1) DiskWarrior 5.2 is compatible with High Sierra, Mojave and Catalina when rebuilding external Mac OS Extended disks.

2) Your external drives (including Time Machine Volumes) can be rebuilt as before.

3) The Startup Disk of Macs are converted to APFS (Apple File System) when installing or upgrading to macOS 10.14 Mojave, macOS 10.15 Catalina or macOS 10.13 High Sierra (High Sierra only converts internal Solid State Drives (SSD/Flash).

4) APFS (Apple File System) disks ARE NOT able to be rebuilt. Click here to learn how to identify an APFS disk.

5) In Mojave and Catalina, Time Machine disks cannot be rebuilt with DiskWarrior unless DiskWarrior is given “Full Disk Access” from within the Security pane of System Preferences. Otherwise Time Machine disks must now be rebuilt from macOS Recovery or the DiskWarrior Recovery Flash drive. 

6) The next major release of DiskWarrior will include the ability to rebuild APFS disks. 

7) Click here to join the Mailing List to be notified of progress regarding Apple File System (APFS) support and updates to DiskWarrior.