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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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18 Comments

  • After reading about 20 different articles and Apple’s own guidance that Time Machine prefers APFS (case sensitive) I reformatted a new SanDisk 2TB G-Drive from HFS+ to APFS (case sensitive) format with single container and two volumes, 1TB each for both reserve and quota; one for files and one for TM Backups. All went well until I tried to select the TM backup volume I created. The drive and volumes don’t show up as disk selection options. I’m on a 2019 MacBook Air (APFS) running Mojave (10.14). I see the volumes in Finder and in the exclude list for TM, so clearly it sees them. They just don’t show up when trying to select them as a backup disk. What gives?

  • A little late to the party, but I ran into some issues and wanted to share my findings and solutions. As background, I have 3 macs and have a variety of backup strategies going. I have a Time Capsule, a QNAP NAS, and local SSD drives that I connect to the Macs. I have always had the SSD formatted as “Mac OS Extended (Journaled)” and have been able to back up multiple Macs to a single SSD. This results in a top level Backups.backupdb folder and inside are the backups for each computer stored in folders named for the computer.

    I JUST moved my 2015 MBP to Monterey 12.4 and bought a new Samsung 2TB SSD to back up it and my old 2012 MBP running 10.14. The first step was to format the drive in the old format, which went as planned. However, I was shocked to find that when I started the backup, Time Machine re-formatted the drive as APFS! Upon completion I found that there was no top level folder. Further, I found that when I moved the drive to attempt a backup on my 2012, I got a message saying that the disk needed to be re-formatted. It turns out that each Volume can only have backups for a single computer.

    A thought a solution might reside in the Container/Volume architecture, where I could create a second Volume in the SSD’s single Container, so I created one after the first backup had been completed. I was able to create it and thought it would be a good solution since the Volumes are dynamically sized. Unfortunately, after doing so, the 2012 did not offer the new Volume (or the old one) as a valid backup disk.

    It seems like the rules are:

    When presented with a new disk, TM will format it as APFS. You can’t use the older format.
    A TM SSD will have a single container that takes up the entire drive and can only contain a single backup Volume, though it seems like you may have other Volumes for other purposes.

    My solution was to re-format the drive as “Mac OS Extended (Journaled)” and then to create a backup on my 2012 running 10.14. I then selected the drive on my 2015 MBP and was able to go back to the old way of working with a single driving backing up multiple machines.

    It’s really sad that it has to be this complicated and that Apple would introduce a new drive strategy that is much more limited than the previous one, but they frequently do things like this, so I’m not surprised.

  • I currently have a 2013 MacPro, OS Mojave 10.14.6, formatted HFS+.
    I don’t know why it never formatted itself to APSF but, it didn’t.
    I’m unable to upgrade to any higher versions of MacOS for some reason. They are not available. And, the only software update option is OS Monterey which won’t install on my HFS+ formatted system.
    Dilemma.
    I’m also trying to understand HFS+/APFS compatibility.
    If I reformat my main boot drive to APFS – erasing the drive – then install OSMonterey – will my HFS+ formatted Time Machine data be readable/available?

  • I have a new Seagate 6TB external. I formatted it APFS (Case-sensitive, Encrypted). And when running Time Machine I specify to encrypt the backup.

    Now when I try to copy other files to the disk I can’t. The disk is showing ‘You can only read’ when doing a Finder Get Info.

    • I too have the same issue , my disc has developed an error now and I’m trying to copy off the old backups onto a new time machine drive and it won’t allow me, all the time machine drives show read only even though a new time machine disc that i bought which is backing up ok , but shows read only. Not sure how to copy off my old time machine backups . Have tried 3 different drives, has apple changed something

  • Really interesting . I stumbled on this article because I am struggling with a recent problem. I used to have two iMacs (one older than the other) successfully networked together. Presumably from what I have just read they both used HFS. . Recently one of them had its power supply go so I decided it was time to get a new iMac. I thought I was buying essentially the same as before i.e. another 21.5” iMac. But I can’t get them to network properly. The new one can see the old one, but the old one can’t connect to the new one. Now I learn that the new one must be the new Apple file system.. it’s really frustrating as each has several HD connected to them with home made videos and over 70000 photos. Seven external hard drives in total. Do I have to just grin and bear it or is there a work around? Finally I am 77 years old, not stupid but definitely not a computer nerd! Any help in layman’s terms please!

    • I don’t think that your problem relates to the hard drive format of your respective computers. I have a 2019 Mac Pro with Catalina and an APFS formatted SSD networked to a Core Duo iMac running with Leopard and an HFS spinning hard disk.

      Unfortunately, I have no idea what your problem is.

  • 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.

    • You’re right, davidb… that line is obviously incorrect. And contradicted twice, later on in the same article:

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

      “… 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 [new backup] 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.”

      I’m about to migrate from a High Sierra system to a new Monterey system, and I’m trying to figure out whether I can continue to use the same external USB, HFS+ formatted Time Machine drive with this new Mac. This article did not clarify anything for me. I’m sorry to say it’s very badly written.

      I understand that both Big Sur and Monterey will continue to recognize, and back up to, HFS+ Time Machine drives (“Time Machine 1” drives), according to this Apple support article:

      https://support.apple.com/guide/mac-help/types-of-disks-you-can-use-with-time-machine-mh15139/mac

      Can anyone tell me from experience whether this is true of Monterey? Thanks.

      • On second reading, I guess Sellers meant that INTERNAL drives need to be APFS, not HFS+, in order for Time Machine to be able to recognize them, and to back up their contents. The text really should be made clearer.

    • The author must mean your Mac’s internal volume(s) have to be APFS, not HFS+, in order for the new Time Machine (“Time Machine 2”) to recognize them, and back up their contents.

  • 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?