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The issues with macOS Big Sur, Time Machine, HFS volumes, and APFS

If you’ve updated to Big Sur and notice that you no longer see one of your Time Machine volumes, it didn’t disappear. Chances are your volume was HFS+, or some other incompatible format. Here’s the background.

About APFS

APFS is the default file system in macOS High Sierra and later for Macs with all-flash storage. I’m guessing this will hold true when macOS Monterey is released. APFS features strong encryption, space sharing, snapshots, fast directory sizing, and improved file system fundamentals.

When you install macOS High Sierra and later on the built-in solid-state drive (SSD) of a Mac, that drive is automatically converted to APFS. Fusion Drives and hard disk drives (HDDs) aren’t converted. You can’t opt-out of the transition to APFS. If you install APFS on any Mac that uses a solid-state drive (SSD) as a built-in boot drive, it will automatically convert to APFS and you will not have a choice. Older Macs that use Fusion Drives or regular hard disk drives (HHDs) will not be converted. 

Apple has promised APFS support for Fusion Drives, but, as best I can tell, this hasn’t happened yet. And no new Macs ship with a Fusion Drive. (By the way, a Fusion Drive was a storage option on some iMac and Mac mini computers that combined a hard drive and flash storage in a single volume.)

With macOS Big Sur, you’ll need a drive formatted with APSF (Apple File System) to use Time Machine for backing up your files (and you really should be backing up your files). If you have existing HFS volumes, you won’t see them after you update, so you shouldn’t update any such volumes. 

Why? There’s no way to convert an HFS+ Time Machine volume to one that uses APFS without erasing it.

As noted by Macworld, before you format a Time Machine drive to APFS, you should note that your old HFS+ based Time Machine volumes remain valid and readable in Big Sur. You can set up a drive from scratch with HFS+ to create new Time Machine volumes as well. 

However—and this is the big “gotcha”—if you want to shift a drive from HFS+ to APFS, you have to reformat the drive. That erases all the Time Machine backups. Macworld notes that, because of the structural differences, you can’t just copy from HFS+ to APFS, either.

The article also points out that:

° Big Sur APFS-based Time Machine backups can’t be used in Catalina or earlier releases. This probably only affects a handful of people, but you’ve been warned. 

° You can share the Time Machine container with volumes that aren’t being used for backups.


Apple’s recommendation

Apple recommends that you work with file formats that work with the company’s Disk Utility. This makes sense as that’s likely the tool you’ll use when formatting, diagnosing, etc., any Mac drives. 

In a support document, Apple says that you should choose one of the following APFS formats for Mac computers using macOS 10.13 or later.

  • APFS: Uses the APFS format. Choose this option if you don’t need an encrypted or case-sensitive format.
  • APFS (Encrypted): Uses the APFS format and encrypts the volume.
  • APFS (Case-sensitive): Uses the APFS format and is case-sensitive to file and folder names. For example, folders named “Homework” and “HOMEWORK” are two different folders.
  • APFS (Case-sensitive, Encrypted): Uses the APFS format, is case-sensitive to file and folder names, and encrypts the volume. For example, folders named “Homework” and “HOMEWORK” are two different folders.

You should choose one of the following Mac OS Extended file system formats for compatibility with Mac computers using macOS 10.12 or earlier.

  • Mac OS Extended (Journaled): Uses the Mac format (Journaled HFS Plus) to protect the integrity of the hierarchical file system. Choose this option if you don’t need an encrypted or case-sensitive format.
  • Mac OS Extended (Journaled, Encrypted): Uses the Mac format, requires a password, and encrypts the partition.
  • Mac OS Extended (Case-sensitive, Journaled): Uses the Mac format and is case-sensitive to folder names. For example, folders named “Homework” and “HOMEWORK” are two different folders.
  • Mac OS Extended (Case-sensitive, Journaled, Encrypted): Uses the Mac format, is case-sensitive to folder names, requires a password, and encrypts the partition.

Finally, you should choose one of the following Windows-compatible file system formats if you are formatting a disk to use with Windows.

  • MS-DOS (FAT): Use for Windows volumes that are 32 GB or less.
  • ExFAT: Use for Windows volumes that are over 32 GB.

Time Machine still supports backups on Mac OS Extended format (Journaled), Mac OS Extended (Case-sensitive, Journaled), and Xsan formatted disks.

To summarize

APFS disks are the preferred format for a Time Machine backup disk. If you select a new backup disk that’s not already formatted as an APFS disk, you get the (one and only) option to erase and reformat it. However, if the disk is a Mac OS Extended format disk that contains an existing Time Machine backup, you aren’t asked to erase and reformat the disk.

For those who still want more tech tidbits about APFS:

° Devices formatted as Mac OS Extended (HFS+) can be read from and written to by devices formatted as APFS.

° Devices formatted as APFS can be read from and written to by:

  • Other devices formatted as APFS
  • Devices formatted as Mac OS Extended, if using macOS High Sierra

° FileVault volumes are converted from Mac OS Extended to APFS, just like unencrypted volumes.

° Boot Camp doesn’t read from or write to APFS-formatted volumes.

° Volumes formatted as APFS can’t offer share points over the network using AFP.

° APFS supports SMB and NFS, with the option to enforce only SMB-encrypted share points.

° You don’t need to change any Time Machine settings to back up APFS-formatted disks. Any Time Machine share points must be shared over SMB instead of AFP. In other words, for most folks, Time Machine will work as usual with no changes.

Have you noticed any oddities with your Time Machine Backup

Dennis Sellers
the authorDennis Sellers
Contributing Author
Dennis has over 40 years of journalism experience and has written hundreds of articles. For the past 20-plus years, he's been an online journalist, covering mainly Apple Inc. He's written for MacCentral, MacWorld, MacMinute, Macsimum News, Apple Daily Report, and is now contributing editor at Apple World Today.
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8 Comments

  • What are we expecting with Monterey? We will be forced to reformat any HFS+ extended Time Machine Backups?

  • So my Time Machine external hard drives are formatted as Mac OS Extended and work just fine with Big Sur. So why would I want to reformat and move to APFS?? Is there an advantage I’m not aware of?

  • If I’ve just set up an Akitio server with 2 SSD drives to serve as Time machines for my 3 Mac computers, will I have problems if the server drives are formatted FAT32? I haven’t backed up my one laptop running Big Sur to this server yet (it still has a portable back up drive). The other two computers are running High Sierra. They seem to be backing up okay, although fairly slowly.

    I had expected to just take my portable Time Machines and put them into the Akitio 2 bay server, but apparently it needed to have the drives reformatted to its own format.

  • Actually, if using a Drobo NAS share for use with Time Machine, the share must be AFP, and will not work with SMB. This is with Drobo Dashboard 3.6.1, the latest version. I have informed DroboPix Support that AFP is depreciated, and will not be supported in a future version of macOS.

  • Thanks for the interesting article. Yet, I have found that

    ° Devices formatted as APFS can be read from and written to by:

    • Other devices formatted as APFS

    does not work in all instances. For instance, external booting disks with macOS 10.15.7 (19H1417) Catalina do not show in macOS 11.6 (20G165) Big Sur.

  • “With macOS Big Sur, you’ll need a drive formatted with APSF (Apple File System) to use Time Machine for backing up your files (and you really should be backing up your files). If you have existing HFS volumes, you won’t see them after you update, so you shouldn’t update any such volumes.”

    Sorry if I am being dense, but I don’t understand this. After updating from Catalina to Big Sur, my Time Capsule drive formatted HFS+ is still visible in System Preferences, the Finder sidebar and Disk Utility, and is still active as a backup.

  • I have two questions. First, I have a Time Machine on Catalina using a Mac OS extended formatted hard drive. If I understand what you’ve written, I can’t copy this Time Machine to an APFS formatted hard drive, and yet it can’t be seen in Big Sur. Is that correct? Can I make the transfer while I’m still using Catalina? Surely, there is a way to not lose all of the backed-up data!

    Second, can Big Sur read and write to hard disks formatted Mac OS extended, or must all external hard disks be reformatted to APFS?

    Thanks!

  • I am a technically challenged senior and you lost me early on so I don’t know if I have a problem or not. I recently bought a M1 24″ iMac from Apple and an external drive recommended by OWC to use as my Time Machine. For the first few months I ran into that “Disk Not Ejected Properly” message very frequently. 2 updates ago, that message disappeared and all seems well. Question is with your post, would I know if there is a problem with this set up?