Tuesday, April 28, 2020

APFS Sparse Bundle Bugs

Howard Oakley:

One of the strangest and most irritating bugs with sparse bundles in APFS format is the unreliability of their estimates of size and free space. Whether you look at free space shown in the Finder or in Disk Utility, there is no correlation between what is shown and what is actually available for use in the sparse bundle. For example, the smallest APFS sparse bundle allowed is 8.4 MB, which is stated as having 8 MB of free space. Yet you’ll find it impossible to copy a 7 MB file to that sparse bundle, as you’ll be told that it’s full even when it’s completely empty. macOS simply refuses to let you use the claimed free space on APFS sparse bundles, although HFS+ sparse bundles aren’t as unreliable.


Despite their widespread use and advantages, macOS features supporting the use of APFS-format sparse bundles are at present riddled with bugs (I count 6 above) and have serious shortcomings. Their inability to self-compact is a major failing which makes their use clumsy at best, and Disk Utility’s lack of support for basic maintenance functions through the last 2.5 years reflects badly on Apple’s engineering priorities. Disk Utility remains of early beta-test quality and far from complete.

I don’t see much reason to use APFS disk images, except for testing how an app works with APFS. HFS+ sparse bundles are dependable and can be compacted with DropDMG.

The Disk Utility reliability problems go back to the rewrite in macOS 10.11. Usually the command-line tools work better.


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I think the main reason that folks switch to APFS images is that it's the default on the current OSes. If you just use hdiutil on a folder it's what you get.

Our distribution image type changed to APFS because of this. The only real negative feedback we've received has been from one customer that was using a Windows utility to mount the disk and it apparently didn't work with APFS yet. (His comment to us that, "You can't assume all your customers have a Mac!!" was curious given that we are an all Mac company that only sells software for macOS. And yes, the email was littered with exclamation points.)

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