OS X comes with a variety of tools and utilities for managing your system (available in the /Applications/Utilities/ folder), including those for observing OS activity, network and disk activity, and also those for managing some aspects of the hardware in your system. One of the most commonly used utilities is Disk Utility, which allows you to create disk images, burn DVDs and CDs, as well as manage the partitions and formatting of your hard drives. Disk Utility comes both in the form of the Disk Utility application, but also as the "diskutil" terminal command.
The Disk Utility application is built to be relatively straightforward and allow you to see each device and add, resize, or remove user-accessible disk partitions as is needed for a particular drive. The diskutil command, on the other hand, is far more robust and can display and manage much more detail about a hard-drive device. For instance, if you enter the command "diskutil list" in the Terminal, the system will show you an output of each drive device along with all partitions that are on the device, which can be convenient for sizing up and checking out any hidden partitions. If you open Disk Utility, however, it will only show the user-accessible partitions and not all of those that are shown with the diskutil command.
Despite these differences, there are some ways to enhance the Disk Utility application's capabilities so you can manage more partitions without needing to use the Terminal. In a recent post on OS X Lion's hidden recovery partition, I demonstrated that Disk Utility can show these hidden partitions, and some people have wondered exactly how to do this.
This setting is a hidden feature in Disk Utility that can be enabled by first enabling the program's "Debug" menu, which is an option that is more suited for development purposes and not for general use. Nevertheless, to enable the menu, just enter the following command in the Terminal, which will edit the Disk Utility preferences file accordingly:
defaults write com.apple.DiskUtility DUDebugMenuEnabled 1
Now relaunch Disk Utility and you should be able to see the hidden partitions by choosing "Show Every Partition" from the now-present "Debug" menu. Do keep in mind that editing hidden partitions may not be a good idea in most situations. The GUID partition scheme that OS X uses always will have a hidden 200MB "EFI" partition as the first partition on the drive (s1), which is used to manage the drive and its partitions in systems with EFI firmware (which is what all Intel Macs use). Beyond this, the OS X 10.7 Recovery partition is also required for managing the new version of FileVault, so if you edit this partition on a FileVault-enabled volume then you may break the encryption keys stored on it and not be able to boot your system or read any data from it.
This option should work Disk Utility for prior versions of OS X as well, so if you are running Snow Leopard or Leopard then you should also be able to manage your partitions with this tip in those operating systems.