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Sunsetting CoreStorage
In macOS 28 and later, the Mac OS Extended file system format will be supported only for volumes (disks and other storage devices) that aren’t encrypted. For future macOS compatibility, either decrypt or reformat any encrypted Mac OS Extended volumes.
I think Apple removed the user interface for creating such volumes way back in Big Sur. It’s not really surprising that they’re going away, although only offering a year of warnings seems rather aggressive. Many people delay updating to major OS versions or wait until they get a new Mac. There will be users that switch to a Mac that can only run macOS 28 and get rid of their old one before realizing that some drive they haven’t connected in a while won’t mount.
The other surprising part is that Apple’s options—reformat or decrypt—are not great. During the initial transition to APFS, macOS would transparently convert an encrypted HFS+ boot volume to encrypted APFS without rewriting any data. This functionality is nominally still available via the diskutil apfs convert command, but Apple hasn’t mentioned this or built an automatic upgrader GUI.
[Decrypting] doesn’t apply to encrypted Time Machine backup disks.
It’s obvious why. The old Time Machine format with hard links is totally different from the new one based on APFS snapshots. But this means that you’ll either need to buy a new Time Machine drive for use with macOS 28 or delete your backup history. Even if you keep the old drive, you’ll need an older boot drive or an old Mac in order to be able to access it.
Previously:
- Searching Time Machine Backups and Versions
- macOS 27 Golden Gate Announced
- macOS 27 to Drop Support for AirPort and Time Capsule Backups
- Removing Unwanted APFS Time Machine Backups
- Should You Continue Using HFS+?
- Time Machine Evolution and APFS
- SuperDuper 3.3 for Catalina
- APFS to be Mandatory for SSDs in High Sierra
Update (2026-07-24): Marcus Mendes:
Apple has now revised the page to add a third option, allowing users to convert an encrypted HFS+ volume directly to encrypted APFS without decrypting it first.
[…]
The company has also removed its previous instructions for decrypting the volume first, converting it to APFS without erasing it, and then optionally re-encrypting it.
Ignore Apple’s guidance and do not use Convert to APFS in Disk Utility for disk images.
The first encrypted HFS+ disk image I tried to convert that way failed and left me with an unusable disk image. If I didn’t have backups I’d have lost its contents.
It didn’t corrupt the disk images that I tried, but it didn’t work, either, instead failing with an error about expecting a GPT partitioning scheme.
Update (2026-07-28): Howard Oakley:
As encrypted disk images have never used CoreStorage, withdrawal of support for that has no impact on the continued use of any form of encrypted disk image, including those using HFS+ as their virtual file system.
This is a good point. Apple’s support page refers to “encrypted Mac OS Extended disks,” but the developer release notes refer to CoreStorage specifically. So this shouldn’t affect most encrypted disk images, which show up in Finder as unencrypted after mounting. The encryption is at the disk image level rather than at the file system level. However, I’m not sure that all encrypted disk images are safe. Presumably, a device image, which directly copies the blocks rather than the files, would still use CoreStorage.
