Time Machine can’t make use of Apple File System (APFS) volumes. This is a significant problem that many Macworld readers want to make sure others know about. This has been known for months, and because you typically have to take steps to convert a drive to APFS, it hasn’t been an issue for most people.
You can accidentally convert a drive to APFS without macOS warning you that you’re about to do so. If you use the Finder option to encrypt a drive in High Sierra, macOS converts the format to APFS before encrypting.
Macworld reader Chee had this happen to them, and wrote in to ask:
Is there a way to undo this process, or at least recover my Time Machine backup going back 2 years and re-setup my external HD?
Yes, although it’s a pain in the patootie, because while converting from HFS+ to APFS and encrypting a drive are all non-destructive and happens in place, converting back to HFS+ requires erasing everything on the disk. Here’s how to make this happen:
- Obtain a new disk big enough to hold the existing Time Machine backups.
- Format that disk for HFS+.
- Follow the instructions in this article to copy your Time Machine backups from the APFS formatted disk to the HFS+ formatted one.
- Enable Time Machine on the APFS disk.
- macOS will prompt you to erase the disk and reformat it as HFS+. Click Erase.
- When the drive is ready, turn off Time Machine, and copy the backups back from the HFS+ disk you used in step 3.
Ask Mac 911
We’ve compiled a list of the questions we get asked most frequently along with answers and links to columns: read our super FAQ to see if your question is covered. If not, we’re always looking for new problems to solve! Email yours to email@example.com including screen captures as appropriate, and whether you want your full name used. Every question won’t be answered, we don’t reply to email, and we cannot provide direct troubleshooting advice.