With the release of macOS High Sierra and its upgrade for SSD-based startup volumes to Apple File System (APFS), Macworld readers had many questions about how this new filesystem—more efficient and reliable for SSDs—will interact with older Macs, hard drives, networked filesharing, and more. Here are the answers.

Many questions revolve around a concern that files stored on an APFS-formatted volume won’t be readable or usable elsewhere. Generally, a filesystem structure only affects the way in which documents are stored on a drive. When the files are retrieved, they’re independent of that format and can handled just as they would in any other case, like downloading a file from a website.

Can I opt to not install APFS?

No. It’s mandatory on SSDs when you upgrade to High Sierra. Fusion drive support (Apple’s hybrid SSD and HDD combo) is coming and, we assume, mandatory with the upgrade that carries it.

Is APFS a reason to avoid upgrading to High Sierra for now?

Opinions vary. It’s an entirely new filesystem if you have an SSD startup drive, and I generally recommend most people wait until there’s a “dot” release, in this case 10.13.1 or even 10.13.2, to ensure any glitches found by early adopters are fixed without you living through the experience. (Since some games and software, like Adobe InDesign, isn’t working correctly with High Sierra at the moment, that’s another reason to delay.)

Once High Sierra upgrades my startup volume APFS, can I revert to HFS+?

A reader having problems after upgrading to High Sierra wonders if APFS is the problem and, if so, can they revert? You can’t: High Sierra doesn’t have a back-out mechanism.

You should make a clone (see next entry) if you want to have the option to revert back to Sierra. This will require wiping the drive, reformatting it, and then restoring the clone.

Can I use cloning software to back up my drive?

Yes, but with provisos. Folks who develop cloning software for macOS are on the front lines of coping with these changes. Dave Nanian of Shirt Pocket, makers of SuperDuper, has a beta release out (free to existing owners) that supports APFS volumes, but on his blog he advises general users against upgrading yet. Bombich’s Carbon Copy Cloner, the other popular drive cloning app, has a release version that supports APFS, but notes (as Shirt Pocket does) that Apple has left some features undocumented, and has a long list of resources to read before upgrading.

If you clone your drive routinely, make a full clone before you upgrade, because otherwise you won’t be able to revert on an APFS drive to a previous system that uses HFS+. It also gives you a clean revert position in case of an upgrade failure.