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I'm stuck on upgrading from Mojave to Catalina. (Yes, I'm late to the party.)

My most recent Time Machine backups continue to be from my Mojave system on an HFS+ Mac OS Extended (Journaled) filesystem. I'm trying to move my Mojave system to a new APFS drive so that I can install Catalina. When I do a full restore from my Time Machine backup onto my new hard drive, formatted as APFS, Time Machine changes the file system type to HFS+, which prevents me from upgrading to Catalina.

How do I get unstuck?

I have been running Mojave on an HFS+ filesystem. My original SSD hard drive was not S.M.A.R.T. enough and initial attempts at a Catalina failed with that error. It took a while, but I finally got a new SSD S.M.A.R.T. hard drive, used CCC to copy my existing system onto it, and installed it in my MacBook Pro (Yay!). I was now happily running Mojave on a new drive that was twice as big as my old one. Time to upgrade to Catalina!

Unfortunately, I thought the S.M.A.R.T. issue was all that I had to deal with, so I had naively formatted the new drive as HFS+, as I've been doing with Mac drives for a decade. When I attempted to upgrade to Catalina again, this time it complained about not having an APFS file system. (Feh!)

SO I booted from the old drive in an external case and reformatted the new drive as APFS. (Oops! There was some stuff that wasn't being backed up by Time Machine that I should have saved elsewhere. Oh well...)

I then did a full Time Machine restoration onto the new drive, now with its APFS file system. (I HATE being without my system for so many hours...)

It resulted in the previous multiple days of effort being wasted because the restoration reverted the filesystem back to HFS+! (And of course the Catalina installer won't tell me that until after it has spent some hours downloading the installation files.)

I know that I cannot be in some rare minority of people who somehow ended up with Mojave on HFS+ when they wanted to upgrade to Catalina. Yet I haven't found the questions and answers about how to get around the seeming Catch-22.

Is keeping Time Machine from reformatting the drive the right question?

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    Surely if you start with a clean install of Catalina on your new SSD (as APFS), then you can use Migration Assistant to bring everything over from your TM backup? It shouldn't matter what the format is.
    – benwiggy
    Apr 5 at 9:38
  • Thanks @benwiggy, I am totally unfamiliar with Migration Assistant. I am optimistic from the name and your suggestion of its use that it may be exactly what I am looking for: a way to restore from Time Machine without overriding the filesystem format.
    – August
    Apr 6 at 21:43
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    When you start up a brand new, 'clean' disk, it asks you if you want to migrate apps, documents and user settings from another Mac, or a TM backup. You just follow the steps. It does a very good job.
    – benwiggy
    Apr 7 at 8:20

2 Answers 2

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Mojave will boot from HFS if you forced the format, though it won't install to it & wants to be on APFS. Catalina is APFS only. Both still use Time Machine formatted as HFS though.

Have you kept your Time Machine clean & away from Catalina interference, or has it 'seen' it? If it's never seen it, clean install Mojave - on APFS - then migrate from Time Machine. Then upgrade to Catalina.

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    Thanks, Tetsujin. The drive has been HFS+ since I bought the computer used in 2015 with El Capitan on it. I have upgraded to Sierra, High Sierra, and Mojave. I don't recall the file system being an issue when I upgraded to Mojave. No, my Time Machine backups have never been seen by Catalina because I have never gotten Catalina installed. Every installation attempt (several, using both Software Update and a downloaded installation app) has failed.
    – August
    Apr 5 at 7:59
  • BTW, my system was originally almost 600GB and my Time Machine restoration is 405GB. Do you know how I might find out what the differences are, especially now that the original has been erased in the APFS reformatting?
    – August
    Apr 5 at 8:00
  • You can't tot up a Time Machine drive like that. It's all hard links, little adds up to make any sense. Anything that's missing now… is missing.
    – Tetsujin
    Apr 5 at 8:02
  • I still have the old drive from before the swap. It has about 520GB on a 525GB drive. In the time between swapping drives and attempting the upgrade, I added about 60GB (two versions of XCode, some movies, etc.) Can I easily compare the two drives, the old one from over a month ago and the current TM restoration?
    – August
    Apr 5 at 8:07
  • It's doubtful. You can always hand-pick bits out of one after the fact.
    – Tetsujin
    Apr 5 at 8:09
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It seems there is NO way to force Time Machine to accept the existing filesystem IF you are doing a full Restore from Time Machine, booting from the Restore partition.

However, Migration Assistant will restore from a Time Machine backup to a different filesystem type than existed when the backup was made.

That is essentially the answer to the original question.

The question, however, was actually an attempted solution to the issue of getting an existing OS installation and user data from a HFS+ filesystem to APFS intact.

That could likely be done with Migration Assistant, but I didn't try that. Instead I used the method outlined in the comments to @tetsujin's answer:

  • Starting with the working system where Time Machine tossed the APFS file system and recreated the HFS+ file system,
  • I erased my now-spare drive (the one that I had replaced in the upgrade) and created an APFS file system,
  • Used Carbon Copy Cloner to clone the working HFS+ system to the external APFS drive,
  • Rebooted from the external drive,
  • Reformatted ihe new internal drive as APFS,
  • Used CCC to clone the working system to the new internal drive.

At this point I have my working Mojave system on an APFS file system on my new internal drive, which hopefully is now ready for the Catalina upgrade.

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