Macでディスクのパーティション形式をMBRからGPTに変える ref: http://qiita.com/ikuwow/items/4bc3923d8f7f8bfb2da2

file0.txt

$ diskutil eraseDisk JHFS+ SecretDisk GPT /dev/disk3
Started erase on disk3
Unmounting disk
Creating the partition map
Waiting for partitions to activate
Formatting disk3s2 as Mac OS Extended (Journaled) with name SecretDisk
Initialized /dev/rdisk3s2 as a 931 GB case-insensitive HFS Plus volume with a 81920k journal
Mounting disk
Finished erase on disk3

file1.txt

$ diskutil eraseDisk
Usage:  diskutil eraseDisk format name [APM[Format]|MBR[Format]|GPT[Format]]
        MountPoint|DiskIdentifier|DeviceNode
Completely erase an existing whole disk.  All volumes on this disk will be
destroyed.  Ownership of the affected disk is required.
Format is the specific file system name you want to erase it as (HFS+, etc.).
Name is the (new) volume name (subject to file system naming restrictions),
or can be specified as %noformat% to skip initialization (newfs).
You cannot erase the boot disk.
Example: diskutil eraseDisk JHFS+ UntitledUFS disk3

file2.txt

$ diskutil info "Secret Disk" | grep Device\ Node
   Device Node:              /dev/disk3s1

file3.txt

diskutil eraseDisk JHFS+ SecretDisk2 /dev/disk3s1 GPT

file4.txt

$ diskutil eraseDisk JHFS+ SecretDisk2 /dev/disk3s1 GPT
Unknown partition scheme: /dev/disk3s1
IkuosMacmini:imgs2pdf degawaikuo$ diskutil eraseDisk JHFS+ SecretDisk2 /dev/disk3s1
A volume was specified instead of a whole disk: /dev/disk3s1
Specify a whole disk, or instead use diskutil eraseVolume to erase a volume on a specific partition

file5.txt

$ diskutil eraseDisk JHFS+ SecretDisk2 GPT /dev/disk3s1
A volume was specified instead of a whole disk: /dev/disk3s1
Specify a whole disk, or instead use diskutil eraseVolume to erase a volume on a specific partition

file6.txt

$ diskutil partitionDisk /Volumes/SecretDisk2 2 GPT JHFS+ JHFS+
/Volumes/SecretDisk2 does not appear to be a whole disk

file7.txt

diskutil eraseDisk JHFS+ SecretDisk2 GPT /dev/disk3