Carbon Copy Cloner Warns Of Issues With Apple's New APFS

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Carbon Copy Cloner is one of the most popular backup tools used by Mac owners. It can take an image of disk, making it easy to either rebuild a broken system or copy a standard installation across multiple machines. But an issue they have found with APFS spares disk images means the company has pulled support for APFS until Apple fixes the issue with their recently released file system.

Carbon Copy Cloner's (CCC) developer, Bombich Software, says that while adding support for APFS to its software was straightforward, neither them nor Apple noticed a very subtle difference in the way APFS works with sparse disk images. What CCC found was that an APFS-formatted sparsebundle disk image volume showed ample free space, despite the underlying disk being completely full.

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.

That led to discovering two bugs in Apple's "disk images-helper" service.

You read about the specifics of the bugs in a blog published by the CCC developers. And the bug is not CCC-specific. Any application that writes to APFS-formatted sparse disk images is affected.

There aren't likely to be too many people affected by this bug. CCC's analysis suggests the number of affected users is likely to be very small. But if you've used CCC and suffered some unanticipated data loss, then perhaps this bug is the culprit.


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