Apple today released a new support document warning that macOS 28 will no longer support encrypted Mac OS Extended (HFS+) volumes, meaning affected external drives will need to be decrypted or reformatted before updating.
Starting with macOS 28, “the Mac OS Extended File System format will be supported only for volumes (disks and other storage devices) that are not encrypted.” Any encrypted HFS+ drives, such as older encrypted external hard drives, will stop working with the Mac unless users take action before upgrading.
Apple did not give a specific reason for this change. APFS, which natively supports encryption, has been the default file system on Mac since the launch of macOS High Sierra in 2017, and dropping encrypted HFS+ support appears to be another push toward completely retiring the old format.
The transition will begin to appear before macOS 28 arrives. Apple says that starting with macOS 26, a Mac can warn users if it detects an encrypted Mac OS Extended drive that will not transfer to macOS 28 or later, by identifying the affected volume by name.
Users can also check manually through Disk Utility by selecting a volume and looking at the format details listed under its name; a volume showing both “Mac OS Extended” and “Encrypted”, such as “CoreStorage Logical Volume • Mac OS Extended (case sensitive, journaled, encrypted)”, will be incompatible.
Unencrypted Mac OS Extended volumes are not affected. Apple says macOS 28 and later will continue to support them and notes that Mac OS Extended is also known as HFS Plus or HFS+.
For anyone who wants to continue using an affected drive after upgrading, Apple recommends first backing up its contents and then reformatting or decrypting them. Reformatting means erasing the volume and reconfiguring it to APFS or APFS (encrypted) format via Disk Utility, which permanently deletes existing data but ensures that the drive continues to work in future versions of macOS.
Decryption is the alternative for anyone who wants to keep their existing data on disk. This involves connecting the drive, unlocking it with its encryption password, then clicking its icon in Finder or on the desktop and choosing Decrypt, then entering the password a second time to begin the process. Apple notes that decryption “takes time, especially for large volumes,” and that progress can be checked in Terminal.
Once decryption is complete, users can optionally convert the volume to APFS without erasing it via the Convert to APFS option in Disk Utility, and then re-encrypt it if they wish. Apple notes that this decryption path does not apply to encrypted Time Machine backup drives.
