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I know the question of "how should I backup my computer" has been asked and answered but I have some specific nuances and, well, if I knew whether they made a difference I wouldn't be asking.

Late 2012 Mac mini with 500GB HDD running High Sierra. I have an HFS+ partition that has gone bad. It appears the files on the partition are accessible, I just can't mount the drive through DiskUtil, repair it, or boot it. I WAS able to add another partition on which Recovery installed Catalina making that an APFS partition. There's nothing there I care about but it's a workspace. When I booted to the Catalina partition it found the original partition and mounted it as read-only. I am not able to manually access any of my user files there because of permissions. I imagine I could work around that but I'm hoping I won't have to.

I understand the original boot partition is effectively hosed as a boot partition. My intention is to purchase a 1TB SSD to backup to, then reformat the entire HDD and restore the errant partition (as much as it will since obviously there's something wrong with it).

My question, as Professor Barbary would say "in 27 parts", is - what is the best way to go about this? Should I:

  • Tell Catalina I want to make a Time Machine backup of the HFS+ partition to the SDD?
  • Use DiskUtil to make a disk image of the partition?
  • Or use a third party tool to copy the files and file structure to the SDD, and if so, what would you suggest? (There's so many out there, I have no confidence sorting the wheat from the chafe.)

Additionally, should I format the SSD in HFS+ or APFS since the original partition is HFS+? Would Catalina allow me to format the SDD as HFS?

It's been suggested, and I probably will, eventually turn the SSD into a Catalina boot drive and move everything over to make it the primary, but for now I just want to make sure my files are safe.

(Ooo, that suggests another option - making the SDD a boot drive and using Migration Assistant to move everything over from the errant partition? ...since I can't manually mount the drive and there are unknown issues I worry whether Migration Assistant would see the partition, though.)

Thanks to David Anderson for his various inputs that have gotten me this far.

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    Honestly, this isn't "backup" it's "recovery". A backup is something you make before you need it, not after. You're looking at one of the myriad file recovery tools. Disk Drill has a good reputation... & stop messing with the broken drive. Every time you perform any operation on it - even a simple read/write, let alone putting new partitions on it - lessens your chances of recovery. Ideally now you install a new drive, put an OS & recovery tools on it, then recover from the bad to the good drive.
    – Tetsujin
    Dec 4, 2021 at 19:09
  • I truly believe the issue is not mechanical. Something was done with software that corrupted the partition in a way that caused it to not be bootable or repairable.
    – lonadar
    Dec 4, 2021 at 21:41
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    It doesn't matter the cause of the issue. Anything you do to modify its current content reduces your chances of successful recovery. If the file tables were wrong, you could have already written over half your data, just by adding a new partition & corresponding file table.
    – Tetsujin
    Dec 5, 2021 at 12:34

1 Answer 1

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After reviewing a few suggestions, and after some other minor issues (the workspace Catalina partition I had created stopped booting, so I removed it and replaced it with a High Sierra installation), I opted for the following:

  1. Formatted the SSD to HFS+ (since I was using High Sierra)
  2. Downloaded Carbon Copy Cloner through the workspace partition. (Disk Drill, mentioned above, cost more than the drive, while CCC offers a 30 day trial.)
  3. Cloned the original partition to the SSD (took about 4 hours, no errors found).
  4. True to advertising, I WAS ABLE TO BOOT THE SSD.

I haven't browsed every file; I imagine there may be a few lost, but this is still leaps and bounds over reformatting and losing it all. CCC apparently turned the SSD into APFS format, so I went ahead and updated to Catalina by downloading the installer.

As an aside, I did try originally using DiskUtility's "Restore" function to copy the partition, but this failed with errors.

As noted above, the partition had become unreadable due to a software issue. I had manually rebuilt the partition map so felt confident I wasn't going to affect file tables by working in the space outside of the target partition. If this had been a mechanical issue, I would have been far more concerned about using the drive as a workbench which, while not impossible, would have made things more difficult.

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