Time Machine is reformatting drive to Mac OS Journaled instead of APFS!

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Time Machine is reformatting drive to Mac OS Journaled instead of APFS!

I know this sounds crazy but it's true. I have a very old but souped up Mac Pro 5,1, running Catalina, and am trying to finally move on, to a new M4 Mini. I have been using a WD My Book for Time Machine backups, without issue, but as I'm getting ready to migrate, I wanted to make the transition easier. So instead I've taken a SanDisk 2TB SSD external I was using with my MacBook Pro, reformatted it in Disk Utility to APFS, and tried to use that. I want to just make one clean TM backup to keep things simple, also this drive is faster than the old one.

But here's the thing: when I connect it to Time Machine, I get a message that says the disk must be erased, because it's in the wrong file format, so it does so, but (I've done this a couple times now) it changes the format to Mac OS Journaled (according to Disk Utility). And then it either fails to do the backup, or the backup is not recognized by the Mini since it's not APFS.

Each time of course I erase and start over in Disk Utility. Weirdly, sometimes it shows it by [name] below Container #, sometimes not, no idea if that's connected.

This external drive was in APFS before.

I don't see a single previous question about this, so maybe I really am special this time.

Posted on Aug 22, 2025 4:52 PM

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Answer 1

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HWTech

Level 9

68,228 points

Aug 22, 2025 8:39 PM in response to ChicagoAl

ChicagoAl wrote:

Thanks, sorry if I was unclear.

No problem, it happens. I'm sure it was clear for you. I know that I have to be very careful when responding on these forums to make sure others can make sense of what I'm trying to convey. I'm not always successful either.

I had gotten hung up on the APFS thing, not realizing that in Catalina TM was still requiring HFS (Mac OS Journaled). Oddly I had not seen that very obvious answer show up anywhere, I kept seeing 'TM disk must be APFS.'

Most of Apple's documentation is focused on the three most recent versions of macOS. Apple tends to delete & remove references to older versions of macOS instead of archiving some of the more important article. There are a few exceptions such as the one I linked here. It is very frustrating since people tend to need these older reference articles since people do use these older versions of macOS for many years.

Naturally after posting my question here, the problem 'solved itself.' TM created a backup and the M4 Mini accepts it.

Great to hear! It is always nice when things suddenly just work, although it can be frustrating not knowing why.

And the old computer is in fact a Mac Pro 5,1, a 'cheesegrater' from 2009, not all my Apple devices show up on this account. I got it new through AppleCare after my G5 tower failed, and I got that after my G4 tower failed. I enjoyed the DIY aspect of keeping such a solid old computer going for so long, but I'm done with it.

It is nice keeping the older hardware working & performing useful actions. 16 years of use is really good for a computer or any electronics in fact. However, there is always a time to retire them unless you are just maintaining them for historical purposes & nostalgia.

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Answer 2

ChicagoAl Author

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8 points

Aug 23, 2025 8:16 AM in response to ChicagoAl

And if anyone should stumble on this in the future, it's addressed on this page about Catalina: Types of disks you can use with Time Machine on Mac - Apple Support

To make things even more clear: Time Machine on Catalina can RESTORE from an APFS disk, but can only BACK UP to an HFS+ formatted on. (HFS+ includes Mac OS Extended, Journaled or not, etc.) Later OS can restore from HFS+ or APFS, but can only BACK UP to APFS.

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Answer 3

HWTech

Level 9

68,228 points

Aug 22, 2025 6:48 PM in response to ChicagoAl

I got lost in your post. It would help if you separated sections into paragraphs with an empty line between paragraphs. Also, make sure to mention which computer you are using to make this TM backup drive. I see three different computers mentioned unless when you say "Mac Pro 5,1" you meant Macbook Pro. A "Mac Pro" is a desktop tower computer while a MacBook Pro is a laptop (higher end model of Apple's laptop lineup since it is a "Pro").

If you are trying to make a new TM backup drive for your Catalina system, then that TM drive needs to be erased as GUID partition and MacOS Extended (Journaled). Time Machine did not start requiring APFS for the TM backup drive until macOS 12.x Monterey IIRC. I don't know if APFS could be used on the TM drive prior Monterey.

Here is an Apple article for setting up a TM backup drive for macOS Catalina (there is no mention of APFS....actually there is no mention of the file system for the TM backup drive....seems TM takes care of that automatically as you have discovered & mentioned here).

Choose a backup disk and set encryption options on Mac -- macOS 10.15 Catalina - Apple Support

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Answer 4

ChicagoAl Author

Level 1

8 points

Aug 23, 2025 5:21 AM in response to Matti Haveri

The TM drive is MacOS, as (I've learned) that's what TM on Catalina does. At the beginning of this process it had successfully generated a TM backup, but for some reason the M4 Mini wouldn't recognize it. When I looked at the disk in Disk Utility, I saw that the format wasn't APFS and assumed that was the problem. It must actually have just been some glitch--maybe the USB-C cable I used that time was faulty. I kept formatting the disk in DU to APFS then was amazed that TM was changing it, hence my question. But it was just doing what it's supposed to do.

Anyway all's well now. Thanks everyone!

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Answer 5

Aug 23, 2025 9:28 AM in response to ChicagoAl

ChicagoAl wrote:

Thanks, sorry if I was unclear.

I had gotten hung up on the APFS thing, not realizing that in Catalina TM was still requiring HFS (Mac OS Journaled).

Minor correction: HFS+ (Mac OS Extended).

Catalina dropped all support (even read-only support) for the original HFS (no "+").

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Answer 6

Aug 22, 2025 7:05 PM in response to ChicagoAl

When you get the Mac mini M4 installed, use it to set up its Time Machine.

Particularly if this is a patched-up 2010-era Mac Pro running macOS well past its limits.

If the Time Machine archive is the path for the transfer, use whatever the Mac Pro was using; that WD My Book.

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Answer 7

ChicagoAl Author

Level 1

8 points

Aug 22, 2025 7:45 PM in response to HWTech

Thanks, sorry if I was unclear.

I had gotten hung up on the APFS thing, not realizing that in Catalina TM was still requiring HFS (Mac OS Journaled). Oddly I had not seen that very obvious answer show up anywhere, I kept seeing 'TM disk must be APFS.'

Naturally after posting my question here, the problem 'solved itself.' TM created a backup and the M4 Mini accepts it.

And the old computer is in fact a Mac Pro 5,1, a 'cheesegrater' from 2009, not all my Apple devices show up on this account. I got it new through AppleCare after my G5 tower failed, and I got that after my G4 tower failed. I enjoyed the DIY aspect of keeping such a solid old computer going for so long, but I'm done with it.

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Answer 8

Aug 22, 2025 10:28 PM in response to ChicagoAl

ChicagoAl wrote:

Naturally after posting my question here, the problem 'solved itself.' TM created a backup and the M4 Mini accepts it.

Is the drive now APFS or MacOS Extended? Maybe it just took a long time to convert the drive's format? Also notice that Disk Utility does not update some info it displays like GUID vs MBR etc unless it is re-launched.

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