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I want to completely wipe a USB thumb drive, re-partition it, and reformat the partition as ExFAT, not JHFS+. Unfortunately, I used FileVault 2 on it when I made it and that seems to be preventing me from destroying the partition table on the drive now.

In the Disk Utility app I can't save and partition table changes to the drive and I can't format the existing partition as anything that isn't HFS+-based.

From the command line this is what I see:

> diskutil list
/dev/disk6
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS UntitlesHFS            *14.8 GB    disk6

And when I try to erase the disk:

> diskutil eraseDisk ExFAT Files disk6

Unable to begin erase operation: Placing a partition map on a Core Storage logical volume is not supported (-69671)

I can't erase the volume, obviously, because ExFAT wouldn't work with FileVault 2:

> diskutil eraseVolume ExFAT Files /Volumes/UntitlesHFS
The specified file system is not supported by Core Storage for use on a Logical Volume

I do know the password for the drive and can mount it just fine.

How can I wipe this USB drive, repartition and reformat it as ExFAT?

  • Have you tried using partitionDisk device? – l'L'l Jan 17 '14 at 18:18
  • I answered on how to nuke and pave using GPT format, but you could also do the same with MBR format... – bmike Jan 17 '14 at 18:28
  • @l'L'l yes, sorry I didn't mention it, but I did try partitioning it from the command line by FileVault and the logical volume layout appears to be preventing that from working. – Ian C. Jan 18 '14 at 2:50
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You can use diskutil cs list to show the core storage view of things.

Once you have the logical volume UUID for the disk in question, you can use diskutil cs deleteVolume to clean up the reserved space that was allocated to the encrypted data and filesystems. That would allow you to surgically remove the core storage.

You could also unmount the filesystems and nuke/pave the drive:

diskutil unmountDisk disk6
diskutil partitionDisk disk6 GPT ExFAT Files 16g

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