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.
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Ugh. I recently switched my offline/archival backup HDs to HFS+.
On APFS it took 12-24 hours to complete a backup to HDDs; with HFS+ it takes 2-6.
I know, I should just buy some SSDs and hope they don't randomly stop working. Not a great time to buy storage, unfortunately. Thanks, AI techbros!
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.
Use Disk Utility > New Disk Image to create an APFS encrypted disk image, then copy all the contents of the old to the new in the Finder. Also annoying: For sparse bundle images, the Finder misreports the size of your new disk image until you demount and then mount it again (and sometimes you also have to relaunch the Finder).
@Dan My read is that you can decrypt HFS+ Time Machine volumes but that it’s not very useful. Converting an HFS+ Time Machine drive to APFS wouldn’t be compatible with APFS Time Machine. And it likely wouldn’t be useful for manual restore purposes: since APFS doesn’t support directory hard links, the data probably wouldn’t even fit. I guess if you want to keep an unencrypted backup for long-term storage…
@Michael Conversion of old Time Machine volumes to APFS does not make sense, I get that. My reason for asking is that I have a handful of old backup drives that I still keep for archival purposes. I was considering decrypting them to make them at least readable in the future.
So what am I supposed to do with my encrypted HFS+ hard drives that are connected to my main workstation? They're large drives meant for storage of files that don't require super fast access. They're sensitive enough that I won't have it be unencrypted. I can't just replace them with SSDs because an equivalent sized SSD would be really, really expensive, especially now that the AI bubble has driven up prices.
I could try to reformat the drive as APFS but then it'll be a nightmare to do anything with it because it'll be so slow.
Well, what I'll *probably* do is just not upgrade macOS, because they just keep finding ways to make it worse. But why not at least continue to support reading this format? No other OS forces users to ditch older filesystems that still work great.
@Bri Large hard drives are super expensive now, too. And, even putting aside price, I don’t think I’ve only even seen USB SSDs larger than 8 TB, whereas you can get a single hard drive that holds 24 TB.
I did not have a lot of time to research this. But it appears that while decrypting a Time Machine volume is possible, reverting the same partition from Core Storage to plain HFS+ is not so easy, if not impossible. For conventional volumes there is a command to revert the conversions to Core Storage. Time Machine volumes seem to be somehow special though and don't allow the conversion back to plain HFS+.
No, I'm really not surprised this is happening either and I get it's a burden for Apple to maintain an entire volume manager that's duplicated in their shiny new filesystem, but it does seem rather premature. Also, APFS isn't equivalent because data storage on HDDs is suboptimal (although, TBF, not absolutely terrible on non-bootable and non-snapshot-heavy disks) and there's no support for tiered storage at all ("Fusion Drive").
I'm surprised they haven't already got rid of AppleRAID, for the same reasons.
Just checked, and in fact there's support for tiered storage in APFS which I somehow didn't notice (see output of "diskutil apfs createcontainer").
It might be time to have a clear preference (instead of a secret one) in DropDMG to allow to use APFS as the default for disk images… Especially for encrypted images.
