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I have an ExFAT drive that I recently reformatted & erased, and also used disk utility repair on Mac. When I pop it in a Windows machine, I'm able to view and add files. But the drive appears empty on Mac.

Disk Utility shows:

  • External Physical disk: 15.8 GB used (all)
  • External Physical volume: 5.9 GB used, 15.8 GB free

I'm wondering what is causing this discrepancy (how can there be 15.8 GB free if 5.9/15.8 GB are used)? How can I fix this issue (e.g. make files appear on the drive on Mac)?

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I'm guessing here because of lack of detailed information but I have seen similar problems before.

I think your external drive has a mix of GPT and MBR based partition information, which confused MacOS (and Disk Utility Repair), but, so far, hasn't caused problems in Windows.
I say so far... Windows might start acting up as well, especially as you fill the disk with more data, which might be written, but can't be read back properly.

You best take the safe route here to prevent loss of data.

  • Copy all data of to another medium. (Hopefully nothing is corrupted yet.)
  • In Windows erase the whole disk with the CLEAN command in the DISKPART utility. This insures there is a valid, non-ambiguous, partition table on the disk.
  • After that you can create a new volume on the disk and format it fresh.
    That new volume should also be safe to use on MacOS.
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  • Apple's APFS doesn't provide the best of supports for exFAT. Apple never got the default cluster size right, so sometimes an exFAT external drive can show and display content in Windows and not in macOS, especially if it's been formatted in Windows, or in macOS THEN used primarily in Windows, then back to macOS (I know, it's complicated). Strangely enough, the same drive with an NTFS file format wouldn't pose any issues in macOS. Go figure. – user1019780 May 28 at 10:56
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Disk utility on MacOS shows you the volume and the partition table. As you didn’t provide both MacOS release nor Windows release, I cannot investigate further.

But, it may be possible that your external drive lacks partition table, or has a windows dedicated partition table. Maybe even LVM ? I’m unsure if Windows is able to handle that.

Only Mojave/Catalina are able to use something that looks like LVM on MacOS.

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