Most External drives come preformatted with the Master Boot Record (MBR) partition scheme. If you are formatting your external drive to use as a recovery drive you will need to format to Mac OS X Extended (Journaled)
- Navigate to the Utilities folder by using the shortcut Command-Shift-U in the finder or type in “Disk Utility” via Spotlight.
- Plug your external drive into your Mac (you will then see it appear in both disk utility and your desktop)
- Select the external disc (do not select the volume entry which is below)
- Click the Erase tab
- In the format table please select Mac OS X Extended (Journaled) in the list of options
- Click on Erase and confirm that you wish to do this.
- Once the disk has successfully formatted it should know in the Partition Map Scheme that it is GUID Partition Table.
- To remove the disk click on the eject button and remove once it has fully ejected.