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Backup solution to create disk image to a file

thebart

thebart

macrumors 6502a
Original poster
Feb 19, 2023
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On Windows, there are many backup software, free ones too, that let me image the system drive to a file on an external disk. You can then make a bootable thumb drive to restore the system drive on catastrophic failure. Windows is of course less locked down than Mac OS in this regard, so this is possible

What's the software for that on Mac. I'm aware of CCC and super duper. Can they cooy the disk image to a FILE. I don't want to dedicate an entire drive to back up the system drive, which is only 512gb and only half full. And then restore that file to get the disk back into the snapshot state even if the system drive isn't bootable for whatever reason

Thanks
 
A couple of other things:

The APFS file system can have many volumes on a disk. These are not partitions with a fixed size, they share the free space. So a volume can grow in size as long as there is free space. You can create new volumes on a disk in seconds with Disk Utilities app. (Creating partitions will still require you to set a fixed size.)

The Disk Utilities app also lets you create a disk image (.dmg).

The way it works after Apple changed to APFS and the 'Signed System Volume', the only way to create a working bootable volume on a drive is by using the Recovery mode to install from the cloud, or with a 'bootable usb installer' on an external disk. Apple support guide here:

How to create a bootable installer for macOS​


Any attempt to boot from a file-by-file copied startup volume will not work. All this is for safety and security, and I think it's fine once you get used to it.

I use carbon copy cloner. It lets you create a bootable volume with a "legacy bootable volume creator" - or, you can do it yourself from Recovery mode. Then, I set up CCC to clone my main drive to it. CCC will not copy any system files (because they are on the locked system volume), only the "- Data" volume which contains everything else. So then I have a fresh install of the system and a clone of the user data on my external disk.

Every night CCC updates the - Data volume of the external to mirror my internal, the system part is never touched, it's locked. If something goes wrong on the internal, let's say I install some software that breaks some functionality, I can boot from the external, open CCC there, and tell CCC to restore my internal to the state it had the night before, or anytime in the past, provided I had it set to use 'snapshots'. (It will also happen very quickly, as CCC only has to restore the new/modified files.) Boot from internal again, and I'm back to where I was yesterday.
 
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I'll just add the because the system volume is read-only, it's virtually impossible for it to become un-bootable. Every Mac running the same OS version has the exact same system volume, bit for bit.
 
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I see. So Mac has a cloistered copy of the OS that can always be restored. That will put it back in pristine mode, I assume the OS it originally came with.

What is the data volume? Is that everything in / ?

Let's say I want to do the minimal backing up. I don't care about the applications which I can always reinstall. Nor do I want to keep a lot of system crud that accumulates over time. Just my documents, system prefs, and app data. Can I just back up /Library and /Users
 
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thebart said:
What is the data volume? Is that everything in / ?
Click to expand...
A bootable mac volume consists of two parts, a 'volume group'. Let's say you call it "MacHD" before installing macOS, after installation it will consist of the read-only system volume called "MacHD", and a full access volume called "MacHD - Data" which contains everything else from apps to user files. This volume group will show as "MacHD" on the computer.

thebart said:
Let's say I want to do the minimal backing up. I don't care about the applications which I can always reinstall. Nor do I want to keep a lot of system crud that accumulates over time. Just my documents, system prefs, and app data. Can I just back up /Library and /Users
Click to expand...
The easy, free way; enable Time Machine. Create a new volume on a disk you want to use for backup, select it in TM. It will not be bootable, but it will mirror the MacHD - Data volume, and be used for restoration. Lots of guides on the web.
Apple support:

Use Time Machine to back up​

 
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thebart said:
Just my documents, system prefs, and app data. Can I just back up /Library and /Users
Click to expand...
You can. The trouble (mess) is that /Library and /Users/xxxx/Library contain not just preferences/settings, but also a great deal of app data. That app data always includes some documents, photos, etc. even if you have taken steps to keep things like photo library elsewhere. And, of course, you have to work out which bits of the Library folders are cached data which does not need backup.

If you just backup all your data (once you have workout where it is) then recovery will involve downloading and reinstalling all your apps, redoing your settings, getting mail back from mail servers, reestablishing any cloud services, restoring the data your have saved (putting it all back in the right places), and the list goes on.

If you want to restore (after a disaster) to the current state, then use Time Machine - just as @Ben J. says.
 
If you use either Carbon Copy Cloner or SuperDuper in their default modes, they'll know what to back up. You have a safe copy of all user data (pretty much everything minus the operating system and cached data). It the worst were to happen and your Macs SSD failed or even if you lost the machine, you will have everything you need to restore a new machine to the same condition.
 
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gilby101 said:
If you want to restore (after a disaster) to the current state, then use Time Machine - just as @Ben J. says.
Click to expand...

Is it possible to set time machine to be less active. Like I want it to back up every day or week, not every hour?
 
thebart said:
Is it possible to set time machine to be less active. Like I want it to back up every day or week, not every hour?
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Yes. It can be set to automatic backups every hour, or day, or week (macOS 14). But, in my experience, it is best left at every hour because then it can make the best use of file system changes without having to scan all your files. I don't notice it running. But try TimeMachineEditor if you have particular needs.
 
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