Watch out! macOS High Sierra could format your Time Machine drive using APFS, and that's not good
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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.
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