Can't ever remove partition?

Running Mountain Lion.

I added a partition with Disk Utility and then had second thoughts about it. I'd like to remove the partition i created, MacSSD2 and hand over its space back to MacSSD. As you can see, the "-" button is disabled even when i select the MacSSD2 partition.

This is the output from command line:

    ~ - Tue Aug 14 10:12:00: diskutil list
    /dev/disk0
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *512.1 GB   disk0
       1:                        EFI                         209.7 MB   disk0s1
       2:                  Apple_HFS MacSSD                  425.7 GB   disk0s2
       3:                 Apple_Boot Recovery HD             784.2 MB   disk0s5
       4:          Apple_CoreStorage MacSSD 2                85.3 GB    disk0s4   <--- Want to remove this
       5:                 Apple_Boot Boot OS X               134.2 MB   disk0s6
    /dev/disk1
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:                  Apple_HFS MacSSD2                *84.9 GB    disk1

~ - Tue Aug 14 10:18:33: sudo gpt -r show disk1
      start       size  index  contents
          0  165900968         

Any clues?

Solution 1:

Looks like your MacSSD2 partition has been turned into a Core Storage volume. Core Storage is Apple's underlying system for disk encryption - I assume you enabled encryption when you created the partition?

You can show the Core Storage volume group using the command diskutil cs list and then delete it using diskutil cs delete <volumegroup-uuid>, where you get the volume group's UUID from the output of the previous command.

That should either delete it entirely or make it deletable in Disk Utility.