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After OS X 10.7 came out with its disk-encryption features, I encrypted an empty USB thumb drive just for grins. I never used it, and eventually decided to reformat it as a normal drive for use with Windows and earlier versions of OS X.

When I opened Disk Utility to try to erase and repartition the drive, however, things looked weird. I clicked on the drive in the left sidebar, but there was no “Erase” tab on the right—only “First Aid” and “Partition”—and the “Partition” tab said, “You may only split this partition into two. To do this, click +.” There was no option to change the partition layout or to remove the encryption from my volume. How can I reformat this drive to remove the encryption?

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up vote 10 down vote accepted

It turns out that Disk Utility didn’t want to touch a disk that contained an encrypted partition, but it had no issue with changing the encrypted partition itself. I clicked on the encrypted partition (not the drive) in the sidebar, and the “Erase” tab appeared on the right. From there I reformatted the disk to Mac OS Extended without encryption, and afterward Disk Utility had no hangups about reformatting or repartitioning the drive.

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Thanks so much. I changed my mind about the partitions I made and encrypted 1 of them. I couldn't go back to change the entire external drive cause of it and I didn't know how to fix it until I found your page. Thanks. – user93762 Oct 6 '14 at 22:35

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