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Original poster
Feb 6, 2016
I have a thumb-drive with sensitive information on it, and I want to do a secure format to erase everything so it cannot be recovered.

I am running Mountain Lion and went into Disk Utility, then selected the drive, then chose Security Options, Secure Erase Options = Zero Out Data, then Erase.

OS-X gives me...

"Disk Erase failed

Disk Erase failed with the error:

Couldn't unmount disk."

I thought maybe my old thumb-drive was dying, so I tried the exact same steps on a brand new thumb-drive and the same issue.


macrumors G3
Sep 6, 2002
Disk Utility said it couldn't unmount the disk. So I asked you to try it manually. Why won't it let you do that? There is only one reason, and that would be that a file is in use from the drive. Try to figure out what that might be. Perhaps quit all running apps except Finder and Disk Utility.
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macrumors 68000
Jun 11, 2009
thumb drives like ssd flash drives can never be securely erased of sensitive data, you are encouraged to encrypt the disk and then throw way the key
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