Can't format USB flash drive as MS-DOS (FAT)

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Level 1

87 points

Can't format USB flash drive as MS-DOS (FAT)

Disk Utility successfully formats my USB flash drives for Mac OS, but fails when I attempt to format them as MS-DOS (FAT). The "Erasing" window says "Erase process has failed. Click Done to continue," and when I click on "Show Details," it says:

Unmounting disk

Couldn't open device.

Operation failed...

I've tried both a 32GB and a 64MB flash drive, to see if size might matter, but it still fails. Any suggestions? Thanks.

MacBook Air, macOS Sierra (10.12.1)

Posted on Mar 30, 2017 10:54 AM

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Answer 1

tjk

Level 9

51,192 points

Mar 31, 2017 2:15 AM in response to dick young1

Hi,

Obviously that should work, and I don't know why it doesn't, but I would try to format the flash drives on another Mac and see if they work, and if so, if your MBA will then recognize them. As another work around, I would try to format them on a Windows machine.

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Answer 2

Jul 9, 2017 10:32 PM in response to tjk

Mine does this on my MacBook Air all the time. I try to format FAT or MacOs Journaled and it errors the first time but then supposedly goes through the second time around ok but when I get it to format the second time and it says successful under FAT, when I insert it into my windows computer at work it says to format and when I do it only gives me about 200mb of free space. If I format the drive via my Mac mini, it formats correctly. What could be causing this issue? Its annoying.

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