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This chapter is from the book

Partition a Hard Disk

Before You Begin

Add a Newly Installed Hard Disk to the System

Back Up Your Information

See Also

Set Up Software RAID

If you've just added a new disk but you don't want it all to be represented as single large volume—but rather to slice it up into several smaller volumes—you can partition the disk.

Partitioning provides a number of practical and psychological advantages; you can designate one volume for video editing, another for MP3s, another for random junk, and a fourth for an alternative installation of Mac OS X. Each of these volumes is mounted as a different disk in the Finder and can be navigated separately, with each volume comprising its own unique organizational structure. This arrangement can be much easier to manage than having a single large volume with folders for different uses.

If your disk has multiple volumes, you can put a different custom icon on each one—and let's face it, custom icons are fun. The more, the merrier!

Figure 3.10Figure 3.10

  1. Open Disk Utility

  2. Open the Finder and navigate to the Applications folder, then to the Utilities subfolder. Launch the Disk Utility program by double-clicking its icon.

  3. Open the Partition Pane

  4. All available disks appear in the listing on the left. Click the disk you want to partition; the Partition tab appears. Click this tab. The Partition pane appears.


    Key Term - Partition—A disk can be uses as a single large volume or be divided into several smaller volumes. This can be done for a variety of reasons, from security to performance to simple organizational preference. Each smaller volume is a partition, and to partition the disk is to divide it into volumes.

  5. Select the Number of Partitions

  6. The displayed disk is most likely represented as a single large, gray pool of storage space. Divide this space in two by clicking the Split button; the pool of space is divided in half. Click Split again to create a third partition, dividing one of the first two areas in half again.


    Practically speaking, you can't partition a disk without losing all the data that's already on it. If you want to divide an existing disk, or change the sizes of existing partitions on a disk, you'll have to resign yourself to the idea that your data will be erased in the process. Some third-party commercial software allows partitions to be resized without data loss, but most such packages don't support Mac OS X.

    Alternatively, you can directly select how many partitions you want from the Volume Scheme menu above the visual representation of the partitions. You can have as many as sixteen partitions on a single disk.

  7. Arrange the Partitions

  8. Here's the fun part: To specify how large each partition should be, simply drag the horizontal dividing bar between two areas and move it up or down. The Size field in the upper-right portion of the window reflects the size of the selected partition; select another partition to see its size.

    To specify a size explicitly, click a partition to select it and type the desired size for that partition into the Size field. You can prevent a partition's size from changing as you fiddle with the other partitions' sizes by enabling the Locked for Editing check box.

  9. Specify Names and Formats

  10. Select each partition in turn and type a name for each one in the Name field; the name you specify here is the name for the volume that's created when you partition the disk. You can specify different formats for each partition, too, in case you want to ensure compatibility with other operating systems; for best results, however, stick with the Mac OS Extended format option.


    You can't partition a volume—you have to select an entire disk from the sidebar. Each volume is, in fact, a partition.

  11. Partition the Disk

  12. When all the partitions are arranged to your satisfaction, click the Partition button. The disk will be erased, formatted, and divided into volumes; after the process is finished, each of the new volumes is mounted in the Finder, ready for you to start using them however you like.


Always back up your hard disk before partitioning anything! The process is straightforward, but that's no consolation if a disk is inadvertently erased.

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