High Sierra: Should you reformat your startup disk now?

If you have decided that you will be upgrading to the first release of High Sierra, an important question is whether to reformat your startup disk now, and if so, whether to use Sierra, the last High Sierra beta, or (if you can) the current Golden Master of High Sierra.

Apple has not yet given any explicit advice on this, but from what it has released so far, the answer depends on what type of drive your Mac boots from.

If your Mac starts up from an SSD (alone, not in a Fusion Drive), then installing High Sierra will convert that drive to APFS format. You have no choice about that. If you have been running beta releases of High Sierra on it, the version of APFS may still need to be updated to that included in the final release, but that should not present a problem to the installer.

There seems no point in trying to force any APFS update early, perhaps from a Golden Master. The final release could still differ from that, and there is no need to get any updating done now.

If your Mac starts up from a Fusion Drive or rotating hard disk, then High Sierra will require that drive to be in HFS+ format. Apple has stated clearly that it does not support the use of APFS on drives other than SSDs in the release version of High Sierra.

If you want to prepare your Mac to install the final release of High Sierra, and your boot Fusion Drive is currently in APFS format, you will need to reformat your Fusion Drive back to HFS+ first. Apple details the process here, and I have explained it in this article.

It should not matter which version of Disk Utility you use to do this, so you could use that from Sierra, a High Sierra beta, a Golden Master, or the final release. If you install macOS in remote Recovery mode, though, you should get 10.12.6 rather than any pre-release version of High Sierra. If you want to go straight to High Sierra, of course, you will need to use a bootable installer containing that release of High Sierra, or wait to make one from its final release.

Of course, if your boot drive is currently in HFS+ format and running Sierra, the High Sierra installer will make the decision for you, and you need to nothing yet, apart from ensuring that the boot drive is in excellent working order, and well backed up.