Apple yesterday published 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 ahead of the update.

Starting with macOS 28, "the Mac OS Extended file system format will be supported only for volumes (disks and other storage devices) that aren't encrypted." Any encrypted HFS+ disks, such as older encrypted external hard drives, will stop working with the Mac unless users take action before upgrading.

Apple has not given a specific reason for the change. APFS, which natively supports encryption, has been the default file system on the Mac since macOS High Sierra launched in 2017, and dropping encrypted HFS+ support looks like a further nudge toward retiring the older format altogether.

The transition will start showing up before macOS 28 arrives. Apple says that beginning with macOS 26, a Mac might notify users if it detects an encrypted Mac OS Extended disk that will not carry over to macOS 28 or later, 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 beneath 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 keep using an affected drive after upgrading, Apple recommends backing up its contents first, then either reformatting or decrypting it. Reformatting means erasing the volume and setting it up again in APFS or APFS (Encrypted) format through Disk Utility, which permanently deletes existing data but ensures the drive keeps working in future versions of macOS.

Decrypting is the alternative for anyone who wants to preserve their existing data on the drive. That involves connecting the drive, unlocking it with its encryption password, then Control-clicking its icon in the Finder or on the desktop and choosing Decrypt, entering the password a second time to begin the process. Apple notes that decryption "takes time, especially for large volumes," and progress can be checked in Terminal.

Source: Macrumors