Apple introduced the Apple Filing System (APFS) file system protocol in macOS Sierra. This is now the required format for macOS, but it took some time to move from the old implementation of the Hierarchical File System Plus (HFS+) format. Even during the transition, Apple kept the old HFS+ standard viable for backwards compatibility. (This is called “Mac OS Extended Format (Journaled)” in Disk Utility.) Macs running versions of macOS as recent as Sonoma can still read volumes in HFS+ format, even if you can’t boot a Mac to from an HFS+ volume from macOS 10.14. Mojave.
Apple also let HFS+ linger for Time Machine backups. It took several versions of APFS-enabled macOS before Apple adapted APFS to encompass a special type of Time Machine backup volume. (This happened under macOS 10.13 Big Sur.)
The company, however, did not provide any transition for existing Time Machine archives. Although you can reformat a standard hard disk drive (HDD) or SSD configured with HFS+ to use APFS instead, reformatting is destructive. You cannot upgrade a Time Machine volume, nor can you copy a Time Machine backup with its archive format intact from an HFS+ volume to an APFS volume and continue backing up there.
How to upgrade a Time Machine drive from HFS+ to APFS
If you’re using Time Machine with an HFS+ drive (which is still allowed with Sonoma), how do you upgrade to APFS, knowing that Apple will likely eliminate Time Machine on HFS+ in a future version of macOS? (Apple generally gives at least two years’ notice, sometimes more, for major changes involving file systems and/or security features.)
The two strategies you have are:
- Start with a clean slate: Reformat your HFS+ drive with the APFS file system, erasing all its data, and immediately perform a full Time Machine backup.
- Remove your HFS+ drive: Since most of us cannot afford to buy expensive and bulky SSDs, you can enjoy the benefits of cheap hard drives. Keep your existing HFS+ Time Machine volume in orange, never modify it, buy a new disk, format it as APFS and start a new Time Machine backup with it. (If you want more protection, you can get two hard drives and set up a RAID 1 mirror, which writes all data to both drives simultaneously.)
A strong caveat: always have a few layers of backups. I do a nightly clone of my startup disk to an external volume, run Time Machine continuously, and also back up my documents to a secure online storage company. Make sure you have at least one full backup before making a significant change, but two is ideal.
The above “clean slate” strategy has the advantage of cost and simplicity. But you lose all previous versions of any file and all deleted files that have not yet been purged. The “remove and replace” approach gives you a deep bench and an extra level of protection as long as that old drive remains in working order and Apple doesn’t abandon HFS+. Even after Apple leaves, you will of course be able to mount and access an HFS+ Time Machine volume on a Mac with an older version of macOS.
This Mac 911 article answers a question submitted by igamesnews reader Eric.
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