Apple’s macOS 27 release notes list Encrypted HFS+ (CoreStorage) as deprecated. The entry reads: “Encrypted HFS+ (CoreStorage) is deprecated and will not be supported in a future version of macOS. If you use Encrypted HFS+ backups on external drives, begin backing up to encrypted APFS-formatted external drives instead.”
A separate Apple support article names that future version. In macOS 28 and later, Mac OS Extended, the format also known as HFS+, “will be supported only for volumes (disks and other storage devices) that aren’t encrypted.” If your Time Machine drive is an encrypted HFS+ disk, now is a good time to plan the switch.
Which drives are affected
Only one combination is affected: a volume that is both Mac OS Extended and encrypted. Apple says macOS 28 “will continue to support unencrypted volumes that use Mac OS Extended format,” and the macOS 27 Mac User Guide says Time Machine “still supports backups on Mac OS Extended format (Journaled)” disks. APFS and APFS Encrypted drives aren’t part of the change.
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Apple’s Time Machine disk page, dated September 14, points at older backup drives in particular: “Some older versions of macOS created backup disks using Mac OS Extended as the file system format instead of APFS.” It sends anyone who chose to encrypt one of those backups to the macOS 28 article.
Your Mac may already have warned you. Apple says that starting with macOS 26, your Mac “might notify you” that you’re using an encrypted Mac OS Extended disk that won’t be compatible with macOS 28 or later, and that the notification identifies the volume by name.
How to check your drive
Apple’s steps use Disk Utility. Connect the drive first.
- Open Disk Utility, which is in the Utilities folder of your Applications folder, or find it with Spotlight.
- From the View menu, choose Show Only Volumes.
- Select the volume’s name in the sidebar.
- Read the information directly under the volume’s name. If it shows both “Mac OS Extended” and “Encrypted,” that volume won’t be compatible with macOS 28 and later.
Apple’s example of an affected drive reads “CoreStorage Logical Volume • Mac OS Extended (Case-sensitive, Journaled, Encrypted).” If you see APFS instead, the drive already uses the format Apple recommends.
If it’s a Time Machine backup drive
Apple lists three fixes for encrypted Mac OS Extended volumes: convert to APFS, decrypt, or erase and reformat. The first two carry the same warning: “This solution doesn’t apply to encrypted Time Machine backup disks.” For a backup drive, that leaves the release notes’ advice to back up to an encrypted APFS drive instead.
Apple’s Mac User Guide says “APFS or APFS Encrypted disks are the preferred format for a Time Machine backup disk,” and that when you choose a new disk that isn’t already APFS, “you get the option to erase and reformat it.” To add one, click the Time Machine icon in the menu bar, choose Open Time Machine Settings, then click Add Backup Disk. If the icon isn’t there, turn it on under Control Center in System Settings.
Reformatting has a cost. Apple says erasing a volume “permanently deletes all data on the volume,” and on a backup drive that means your backup history. If you want to keep that history, set up a second drive as an encrypted APFS Time Machine disk and leave the old drive as it is.
If it’s a regular encrypted drive
Drives you use for files rather than Time Machine have two extra options, according to Apple:
- Convert to encrypted APFS. In Disk Utility, choose View > Show Only Volumes, select the volume, then choose Edit > Convert to APFS and click Convert.
- Decrypt it. Control-click the drive on the desktop or in the Finder sidebar, choose Decrypt, and enter the password again. Apple warns this takes time on large volumes, and the drive stays Mac OS Extended without encryption.
The third option, reformatting as APFS or APFS (Encrypted), erases the drive, so copy anything you need first. For a fuller routine, our guide to backing up your Mac before macOS 27 still applies, and our macOS 27 Golden Gate overview covers what else changed.
