A tale of two Disk Utilities: Sierra and High Sierra

While we’re all thinking about Apple’s software quality assurance, following its recent root user vulnerability, I’d like a few words about Disk Utility.


I’ll start with version 16.3, supplied with macOS Sierra 10.12.6. Although it can usually be coaxed to do most of its tasks properly, it often throws errors and refuses many basic tasks the first time around.

Sometimes, it will format a USB memory ‘stick’ in standard ExFAT without batting an eyelid. But not infrequently, the first attempt fails.


Try again, and it suddenly discovers that it can do it after all, and completes without any error.


In my experience, when it formats a drive, it is pretty reliable. I can use ExFAT and HFS+ drives formatted by Disk Utility 16.3 with Sierra 10.12.6, and High Sierra 10.13 and 10.13.1. So it seems good to use, once you have worked through its annoying habit of first refusal.

High Sierra

Disk Utility 17.0, even build 337 which came with the High Sierra 10.13.1 update, is almost the exact opposite. It tends to refuse some apparently straightforward tasks, like formatting some USB sticks and SSDs in APFS, but for others it blunders ahead and gets them wrong.

Its behaviour with USB sticks is particularly irksome. It tries to format them in ExFAT, but usually seems to make a mess and produce an unusable volume. I have taken to formatting all such sticks in Sierra, even though this means erasing them twice to work through its initial failure; currently that seems to be the only way to do so reliably. After the second release of a major version of macOS, that is hardly acceptable.

The puzzle here is that ExFAT format and USB sticks are hardly novel. Unlike with APFS, there shouldn’t be any need for new code to make Disk Utility work reliably with established formats such as ExFAT and HFS+.

Problems with APFS are more understandable: it is, after all, a brand new file system, and is bound to have teething problems. I still find it impossible to guess what Disk Utility will do when asked to convert an SSD or USB stick to APFS, though. Sometimes it just works, and others its errors are so persistent that I have to give up. There is then no option to fall back to Sierra, whose early implementation of APFS lies abandoned and useless.


For those frustrated by unsuccessful attempts to convert or format solid-state media (SSD or stick) to APFS, the screenshot below is evidence that it can be done, but doesn’t explain why their media fail every time.


I haven’t even got down to problems of detail here, such as why both versions of Disk Utility always state that external drives are not SSDs even when they are, or, worse still, the continuing lack of support for SMART on drives attached by USB.


Is there a more reliable alternative to Disk Utility? Something which provides a comfortable and reliable wrapper for the command tool diskutil would be really useful, please.