Restoring from a .dmg AND .dmgpart file?

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abillmann Author

Level 1

4 points

Restoring from a .dmg AND .dmgpart file?

Mac Mini (Late 2012, i7, 16GB RAM, 2.0TB SSD)

Hey all,

I'm trying to update my Mini from Mojave to Catalina.

Problem is, the 2TB SSD internal HD was formatted as Mac OS Extended (Journaled), but Catalina requires APFS format.

So, I booted from a USB start-up to make a disk image of the internal SSD and save it to another external drive. I started that process late last night and let it run.

This morning, Disk Utility reported that the operation was successful, but instead of a single .dmg file as I was expecting, there were two files: A .dmg and a .dmgpart.

After I reformat the internal SSD to APFS, how do I restore the drive from the .dmg and .dmgpart?

Does it "just work" or is there something different I need to do?

Thanks in advance for help, insights and advice!

Mac mini, macOS 10.14

Posted on Oct 23, 2020 10:12 AM

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Answer 1

VikingOSX

Level 10

127,156 points

Oct 23, 2020 12:21 PM in response to abillmann

Why not perform a Time Machine Backup to an external MacOS Extended (Journaled) formatted drive for safe keeping.

Now, apply the Catalina upgrade from the Mac App Store, and it will detect the HFS+ drive, and non-destructively convert it to APFS, upgrade the operating system, and your original files will be right where they were before the Catalina upgrade. Any 32-bit applications installed prior to the upgrade will be inoperable due to Catalina's 64-bit application requirement.

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Answer 2

Oct 23, 2020 8:41 PM in response to abillmann

First don't use Disk Utility to make a .dmg of a boot volume. Disk Utility is terrible at this. Instead use the third party app Carbon Copy Cloner (CCC) to make a .dmg image of your Mac. CCC will also include the hidden recovery partition as well. I've never had a problem using CCC to clone a macOS boot drive.

After you have a good backup using CCC, then you can try to convert the file system or erase the drive as APFS (top option).

You can try to boot into Recovery Mode (Command + R) and launch Disk Utility to see if it can convert the file system to APFS. If not, then you can try to use the Terminal app and the command line utility "diskutil". In theory this should convert the file system while leaving your data intact like the Mojave installer should have done previously. However, many users report Disk Utility won't convert the file system (no idea if this is true or if the users were doing this incorrectly).

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Answer 3

abillmann Author

Level 1

4 points

Oct 23, 2020 1:07 PM in response to VikingOSX

That's what I hoped would happen. :)

After I initiated the update, it downloaded and launched the updater. Shortly thereafter, a dialog box popped up regarding the volume -- the internal SSD was grayed out, in the typical "This is not an option" style. Hovering over the grayed-out icon, the message "Catalina requires APFS format" or something like that. There were literally no other options other than to choose another volume or quit.

So I figured that meant I would need to reformat the internal SSD and restore it. Did I miss something?

(Also... I do have a full Time Machine backup of the drive, but thought making a fresh disk image would ultimately be faster.)

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Answer 4

abillmann Author

Level 1

4 points

Oct 27, 2020 2:16 PM in response to HWTech

HWTech:

Absolutely masterful advice.

Thank you! I used CCC to make a .dmg of the SSD boot drive (saved to an external drive), reformatted the SSD boot drive to APFS, then cloned the image back from the external drive to the internal. Worked perfectly. (Took a little while, but sure.) I haven't done the update to Catalina yet, but with this problem solved--as well as having a very fresh backup .dmg--I'm sure it will go fine.

Thank you again!

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Answer 5

Oct 27, 2020 6:27 PM in response to abillmann

You're welcome. CCC is a great app and has served us well for years for creating system images just as you've done. I've never used it as an actual app for backups though.

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Restoring from a .dmg AND .dmgpart file?

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