Wednesday, April 17, 2024

macOS 14 Sonoma vs. exFAT

Mike Wuerthele and Malcolm Owen (via Ric Ford):

An issue preventing some external drives from mounting onto a Mac running macOS Sonoma has plagued users for months, and it probably was caused by changes Apple made to drive handling.


Unlike the Windows-preferred NTFS or Apple’s APFS, exFAT can be read from and written to by both Macs and Windows PCs without requiring any extra software assistance. In a multi-platform environment, it’s almost always the best formatting option for external drives.


Shortly after the introduction of macOS Sonoma, complaints started to surface on Apple’s Community Support forum. The complaints featured irate users discovering that their external disks were not reliably being mounted in macOS at all.

It seems like the last few releases of macOS have trouble with mounting external drives in general, even APFS ones. But there may also be an exFAT-specific issue here.

macOS Sonoma 14 Release Notes:

The implementations of the exfat and msdos file systems on macOS have changed; these file systems are now provided by services running in user-space instead of by kernel extensions.


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I had something similar with Monterey and the solution was for me to flash newer firmware to the hard drive enclosure. Whilst researching this, I came across so many posts of people giving up and resigning the data on their external drive lost forever. But this is far from the truth, the data is fine it's just that macOS no longer likes the type of handshake the old firmware is using. The drive/enclosure manufacturer answered my support emails but the response was that they weren't interested in addressing it.

So some users are seeing this with APFS formatted drives as well? But the NTFS/exFAT problem might be specifically related to user mode instead of kernel file system support?

Also, to the commenter on the AppleInsider page, exFAT is not an ancient file format, what a weird take. I presume they have confused exFAT and FAT32. Is 2006 ancient? NTFS is from…1993 maybe? As a comparison. I mean, I mostly used EXT4 and it's largely been in use since 2008, and I've probably been using it for over a decade myself. Can't actually remember when I switched over from EXT3.

@Nathan The APFS problem is longstanding, but lots of people seemed to encounter the exFAT problem only with Sonoma. So it’s reasonable to presume that there are two separate issues, the latter related to the changes in Sonoma.

@Michael Tsai
What's the fix for external APFS drives not mounting? Seems strange external drive mounting is so broken for so long if that's the case.

@Nathan I don’t know of a fix. The problem is that they don’t auto-mount, so the workaround is to manually mount them with Disk Utility. Sometimes it takes multiple tries…

@Michael Tsai
Doesn't automount and manual mount sometimes fails too? Does it make a difference with type of drive? Or enclosure's chipset? Not sure how many external drives you have on hand to test of course. But this is fascinating. Seems like a basic function of the OS is not working.

@Nathan Yes, both automount and manual mount sometimes fail. I haven’t noticed a pattern with around half a dozen distinct enclosure types (not sure of chipsets) and 50 or so drives of different brands. The problem occurs for 2.5-inch and 3.5-inch spinning hard drives as well as SSDs.

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