Disk image creation from folder: error 28 - no space left on device

Question

I wanted to create a full copy of my MacBook Air in a disk image for archive. I can't save the disk from the booted system, so I restarted my Mac in Recovery mode (keys Command and R) on boot. From the recovery menu, I can launch Disk Utility, I select the 'Macintosh HD' drive, give the image a name, select the options "not compressed" and "read only". I select the destination disk and let the process begins... After a long time, just before ending the process, I have a message "error 28: No space left on Device".

My MBA has a 250 GB SSD disk, I have a 50 GB iCloud account, so in the case iCloud Drive is saved too (I don't think so...), there is just about maximum 300 GB to save. I tried to save on a Drobo (which claims being 64 TB in size, and have more than 2TB free), and on an empty 1TB Drive, and had the same result.

Answer 1

Well... It seems that APFS and/or iCloud Drive has killed the ability to create a disk image from an entire disk... I tried lots of things, even Disk Utility's Restore in a freshly-created disk-image failed.

So I did it the hard way, with the terminal

• Creation of a disk image (lot bigger than the drive) hdiutil create -size 500g -fs HFS+ -volname Clone\ Macintosh\ HD /Volumes/WD\ 1To/Clone\ MBA.dmg
• Mounting the disk image hdiutil attach /Volumes/WD\ 1To/Clone\ MBA.dmg
• Note the /dev/disk_s_ path to unmount it
• Save the disk with RSYNC (options and exclusions found on the internet) sudo rsync -vaEx /Volumes/Macintosh\ HD/ /Volumes/Clone\ Macintosh\ HD --exclude=/Volumes/* --exclude=/Network/* --exclude=/automount/* --exclude=/dev/* --exclude=/private/tmp/* --exclude=/private/var/run/* --exclude=/private/var/spool/postfix/* --exclude=/private/var/vm/* --exclude=.Spotlight-*/ --exclude=.Trashes --exclude=*/.Trash --exclude=/afs/* --exclude=/cores/*
• The result was bigger than the original drive (probably due to APFS which have some tricks to not duplicate data when copying a file, and certainly due to the saving of documents that are on iCloud Drive but not really on the disk: icons with a cloud badge)
• Detach the image hdiutil detach /dev/disk3s2
• Then I tried to shrink the disk image from the command-line, but neither hdiutil compact, not hdiutil resize worked (errors)
• Then I tried to resize with Disk Utility, but it didn't work too (disk utility claimed it was done, but the size didn't change at all)
• So I converted the image to read-only with Disk Utility (in fact, it duplicated the image), and now I have a shrinked disk-image of my entire startup disk!

Lot of wasted time, it used to be easyer