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Report: macOS May Lose Data on APFS-formatted Disk Images

In a recent article on the company’s blog, Mike Bombich of Carbon Copy Cloner shared an APFS bug that can cause the loss of data when writing to images.

Bombich describes the bug at length in the blog article and how it was discovered.

“Earlier this week I noticed that an APFS-formatted sparsebundle disk image volume showed ample free space, despite that the underlying disk was completely full. Curious, I copied a video file to the disk image volume to see what would happen. The whole file copied without error! I opened the file, verified that the video played back start to finish, checksummed the file – as far as I could tell, the file was intact and whole on the disk image. When I unmounted and remounted the disk image, however, the video was corrupted. If you’ve ever lost data, you know the kick-in-the-gut feeling that would have ensued. Thankfully, I was just running some tests and the file that disappeared was just test data. Taking a closer look, I discovered two bugs in macOS’s “diskimages-helper” service that lead to this result.”

Bombich states that the issue isn’t likely to affect a large amount of CCC users. However, he added, “Until Apple issues a macOS update that resolves this problem, we’re dropping support for APFS-formatted disk images.” 

You can read more about the APFS bug at Carbon Copy Cloner’s official blog:

Further Reading:

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  • I was withholding the upgrade, now I know why. Hope nobody gets burned to badly with this.

  • I maintain a CCC clone of all my main system drives. I have an APFS 10.13.x experimental drive running for just this reason–(above). CCC has never failed for me…

  • I discovered an issue in that I copied a video file from another drive, used it in Adobe Encore, yet a day or so later the file had disappeared ! This happened more than once!

  • Dang. This stinks! Any word from Apple on fixing this bug? It sounds like I may be one of those affected…

    Thanks for the heads up!

  • This is one reason that I recommend Carbon Copy Cloner — Mike Bombich is punctilious about maintaining the integrity of my backup data.