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I have a 500 GB USB drive, which I once partitioned into two parts: one encrypted—Mac OS Extended (Journaled, Encrypted), and the other not—Mac OS Extended (Journaled).

Now I want to change the partition layout, and probably add a new partition. However, I was unable to do this in Disk Utility: all options related to partitions are greyed out. See the screen cap for example (clicking on the partitions does not work, either). screen cap of disk utility This is pretty weird: not only can't I resize or add partition, I can't make any change to the partition layout, including completely reformatting the disk! Any ideas about this?

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You cannot resize a drive that has been encrypted. You will first need to unencrypt the drive, then resize the partitions, then re-encrypt the drive.

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That is a USB drive, not the Macintosh HD... –  KevinSayHi Mar 6 '13 at 23:21
    
Removed the word FileVault. OS X will not allow an encrypted volume to resized. You may have luck with the command-line diskutil command if you are careful, but it's easier to unencrypt. –  bispymusic Mar 7 '13 at 2:50
    
Thanks, I didn't realize that USB drives are also encrypted with FileVault. This is lame, though. I ended up erasing all the contents to update partition. One thing I don't understand: why don't they allow resizing unencrypted partitions? (Well regarding memory and storage I know nothing beyond virtual memory, so please excuse me if this is a stupid question.) –  KevinSayHi Mar 7 '13 at 5:21
    
If all volumes on a physical drive are unencrypted then you can resize the partitions, provided there is enough physical free space at the end of a volume (Disk Utility shows this as a blue bar within each volume in your screenshot). If a single partition is encrypted and you want to resize another partition, I don't believe Disk Utility will allow you. I am not sure the reasoning, it may have to do with integrity of the encryption and how OS X validates it. That, however, is a guess. –  bispymusic Mar 7 '13 at 13:07
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