Disk Utility (Yosemite): Partition a disk

Partition a disk
Partition a disk using Disk Utility

Partitioning a disk divides it into sections, which are listed as separate disks under the Devices section of the Finder window. You may need to partition a disk if you want to install multiple operating systems on the disk or if you need to change the disk’s format.

WARNING:   To prevent the loss of data on your Fusion Drive, don’t connect it to a Mac that’s using a version of OS X older than v10.8.5. For more information, see the Apple Support article Only connect OS X Mavericks Fusion drives to OS X Mountain Lion v10.8.5 or later.

Open Disk Utility for me

Disks with two partitions

Partition a disk

  1. Select the disk in the sidebar, then click Partition.

    If you’re partitioning an external disk, make sure it’s connected to your computer.

  2. Click the Partition Layout pop-up menu, then choose the number of partitions.

    You can enter a size for each partition or drag the divider between the partitions to change their sizes. If a partition’s name has an asterisk beside it, it’s being shown larger than its actual size so the name can be displayed clearly.

  3. Click each partition, then enter a name for it.

  4. For each partition, click the Format pop-up menu, choose a format, then enter a size.

    • Mac OS Extended (Journaled): Uses journaling to protect the hierarchical file system integrity.

    • Mac OS Extended (Case-sensitive, Journaled): Uses journaling and is case sensitive to folder names. For example, folders named “Homework” and “hoMeWOrk” are two different folders.

    • MS-DOS (FAT): Use for Windows disks that are 32 GB or less.

    • ExFAT: Use for Windows disks that are over 32 GB.

    • Free Space: Use to extend the free space for the disk.

  5. Click Options, then choose one of the following:

    • GUID Partition Table: Choose this partition scheme if you’ll be using this disk only with Mac computers.

    • Apple Partition Map: This partition scheme should only be used if you’re working with Mac computers using Mac OS X version 10.4 or earlier.

    • Master Boot Record: Also known as “fdisk,” choose this partition scheme if you’ll be using the disk as a secondary disk for the Windows operating system you installed using Boot Camp, or for an external disk you’ll be using on a Windows computer.

  6. Click Apply.

After you partition a disk, a disk icon for each partition appears in Disk Utility and in the sidebar of Finder windows.

Create new partitions on a disk containing data

You can create new partitions on a disk that contains data, if it has space available. Each partition works like a separate disk.

Important:  
  1. Select the disk in the sidebar where you want to create new partitions, then click Partition.

    If you’re partitioning an external disk, make sure it’s connected to your computer.

  2. Select an existing partition in the Partition Layout list, then click Add .

    Disk Utility splits the partition into two, leaving the data in one partition, and creating a new empty partition. If the existing partition is less than half-full, Disk Utility creates two partitions of equal size. Otherwise, it creates one partition large enough for the existing data, and another partition with the remaining space. Depending on the space available, you can create multiple partitions by selecting the new partition and clicking Add .

  3. Resize the partitions as needed by doing one of the following:

    • Drag the dividers between the partitions in the Partition Layout list.

    • Select a partition in the Partition Layout list, then enter a value in the Size field.

  4. Select a partition in the Partition Layout list, then enter a name in the Name field.

  5. Click the Format pop-up menu, then choose a format for the partition.

    • Mac OS Extended (Journaled): Uses journaling to protect the hierarchical file system integrity.

    • Mac OS Extended (Case-sensitive, Journaled): Uses journaling and is case sensitive to folder names. For example, folders named “Homework” and “hoMeWOrk” are two different folders.

    • MS-DOS (FAT): Use for Windows disks that are 32 GB or less.

    • ExFAT: Use for Windows disks that are over 32 GB.

    • Free Space: Use to extend the free space for the disk.

  6. Click Apply.

Enlarge a partition

If you have multiple partitions on a disk and one of them is running out of space, you may be able to enlarge it without losing any of the files on it.

To enlarge a partition, you must delete the partition that comes after it on the disk, then move the end point of the partition you want to enlarge into the freed space. You can’t enlarge the last partition on a disk.

WARNING:  
  1. Select the disk in the sidebar that contains the partition you want to enlarge, then click Partition.

  2. In the Partition Layout list, select the partition beneath the partition you want to enlarge, then click Delete .

    The partition is immediately erased, leaving the space it formerly occupied available.

  3. Resize the partition by doing one of the following:

    • Drag the dividers between the partitions in the Partition Layout list.

    • Select a partition in the Partition Layout list, then enter a value in the Size field.

  4. Click Apply.

If you’re partitioning your disk because you want to install Windows, use Boot Camp Assistant.

Open Boot Camp Assistant for me

Last Modified: Feb 20, 2015
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