How to Resize an Existing Volume with Disk Utility

Disk Utility - What You Need to Know About Modifying Existing Volumes

The version of Disk Utility bundled with OS X 10.5 and later has a few notable new features, specifically, the ability to add, delete, and resize hard drive partitions without first erasing the hard drive. If you need a slightly larger partition, or you would like to split a drive into multiple partitions, you can do it with Disk Utility, without losing the data that’s currently stored on the drive.

Resizing volumes or adding new partitions with Disk Utility is fairly straightforward, but you need be aware of the limitations of both options.

In this guide, we’ll look at resizing an existing volume, as well as creating and deleting partitions, in many cases without losing existing data.

If you want to partition and create volumes on a hard drive that doesn’t contain any data, or you’re willing to erase the hard drive during the partitioning process, see the Disk Utility - Partition Your Hard Drive With Disk Utility guide.

What You Will Learn

• The difference between hard drives, partitions, and volumes.
   
• How to resize, add, or delete volumes.

What You Need

• A Mac with OS X 10.5.x or later installed. This guide is specific to OS X 10.5, but it should also be usable with future versions of the Mac OS. Earlier versions of Disk Utility are not able to resize or add to an existing volume without first erasing that volume’s contents. Do not attempt to use earlier versions of Disk Utility for this process.
   

• One or more hard drives whose volumes you wish to resize, add to, or delete.
   
• A few minutes of your time. Partitioning is a quick process. It will probably take longer to read this article than to partition your hard drive.

Published: 7/11/2008

Updated: 1/19/2015

Disk Utility - Definitions of Partitioning Terms

Disk Utility makes it easy to erase, format, partition, and create volumes, and to make RAID sets. Understanding the difference between erasing and formatting, and between partitions and volumes, will help you keep the processes straight.

Definitions

• Volume. A volume is a storage container that has been formatted with a file system your computer (in this case, a Mac) can recognize. Volumes are logical constructs; they’re not the same as partitions or physical hard drives. Volumes are most often made up of a single hard drive partition that contains a Mac file system. But it’s also possible for a volume to be made up of multiple partitions, something we won’t address here.
   

• Partition. The term ‘partition’ is both a verb and a noun. When you partition a hard drive, you physically create separate sections on the hard drive; each of these sections is called a partition. A partition defines a specific area of a hard drive.
   
• Erase. Erasing is the process of removing all data from a specific volume or hard drive. Data can be erased in multiple ways. The default method on the Mac deletes the data table entries for the location of the file, but does not actually remove the file itself from the hard drive or volume. The practical effect of this is that your Mac no longer sees the file, and the space it uses is now marked as available free space. You can also specify optional erase options that will completely remove the data.
   
• Format. Formatting a hard drive defines how the hard drive’s media will be laid out to store the computer data. Your Mac can use five different types of formats: Mac OS Extended (Journaled); Mac OS Extended; Mac OS Extended (Case-Sensitive, Journaled); Mac OS Extended (Case-Sensitive); and MS-DOS.

Published: 7/11/2008

Updated: 1/19/2015

Disk Utility - Resize an Existing Volume

Disk Utility allows you to resize existing volumes without losing data, but there are a few limitations. Disk Utility can decrease the size of any volume, but it can only increase the size of a volume if there’s enough free space available between the volume you wish to expand and the next partition on the drive.

For practical purposes, this means that if you want to increase the size of a volume, you may need to delete the partition below that volume.

You will lose all data on the partition you delete (so be sure to back up everything on it first), but you can expand the selected volume without losing any of its data.

Enlarge a Volume

1. Launch Disk Utility, located at /Applications/Utilities/.
    
2. Current hard drives and volumes will display in a list pane on the left side of the Disk Utility window. Hard drives are listed with a generic disk icon, followed by the drive’s size, make, and model. Volumes are listed below their associated hard drive.
    
3. Select the hard drive associated with the volume you wish to expand.
    
4. Click the ‘Partition’ tab.
    
5. Select the volume listed immediately below the volume you wish to expand.
    
6. Click the ‘-’ (minus or delete) sign located below the Volume Scheme list.
    
7. Disk Utility will display a confirmation sheet listing the volume you are about to remove. Make sure that this is the correct volume before taking the next step.
    
8. Click the ‘Remove’ button.
    
9. Select the volume you wish to expand.
    
10. Grab the right-hand bottom corner of the volume and drag to expand it. If you prefer, you can enter a value in the ‘Size’ field.
     

1. Click the ‘Apply’ button.
    
2. Disk Utility will display a confirmation sheet listing the volume you are about to resize.
    
3. Click the ‘Partition’ button.

Disk Utility will resize the selected partition without losing any of the data on the volume.

Published: 7/11/2008

Updated: 1/19/2015

Disk Utility allows you to add a new volume to an existing partition without losing any data. There are, of course, some rules that Disk Utility uses when adding a new volume to an existing partition, but overall, the process is simple and works well.

When adding a new volume, Disk Utility will attempt to split the selected partition in half, leaving all of the existing data on the original volume, but reducing the size of the volume by 50%.

If the amount of existing data takes up more than 50% of the existing volume’s space, Disk Utility will resize the existing volume to accommodate all of its current data, and then create a new volume in the remaining space.

Add a New Volume

1. Launch Disk Utility, located at /Applications/Utilities/.
    
2. Current hard drives and volumes will display in a list pane on the left side of the Disk Utility window. Hard drives are listed with a generic disk icon, followed by the drive’s size, make, and model. Volumes are listed below their associated hard drive.
    
3. Select the hard drive associated with the volume you wish to expand.
    
4. Click the ‘Partition’ tab.
    
5. Select the existing volume that you wish to split into two volumes.
    
6. Click the ‘+’ (plus or add) button.
    
7. Drag the divider between the two resulting volumes to change their sizes, or select a volume and enter a number (in GB) in the ‘Size’ field.
    
8. Disk Utility will dynamically display the resulting Volume Scheme, showing how the volumes will be configured once you apply the changes.
    

1. To reject the changes, click the ‘Revert’ button.
    
2. To accept the changes and re-partition the hard drive, click the ‘Apply’ button.
    
3. Disk Utility will display a confirmation sheet that lists how the volumes will be changed.
    
4. Click the ‘Partition’ button.

Published: 7/11/2008

Updated: 1/19/2015

In addition to adding volumes, Disk Utility can also delete existing volumes. When you delete an existing volume, its associated data will be lost, but the space the volume occupied will be freed up. You can use this new free space to increase the size of the next volume up.

Remove an Existing Volume

1. Launch Disk Utility, located at /Applications/Utilities/.
    
2. Current hard drives and volumes will display in a list pane on the left side of the Disk Utility window. Hard drives are listed with a generic disk icon, followed by the drive’s size, make, and model. Volumes are listed below their associated hard drive.
    

1. Select the hard drive associated with the volume you wish to expand.
    
2. Click the ‘Partition’ tab.
    
3. Select the existing volume you wish to delete.
    
4. Click the ‘-’ (minus or delete) button.
    
5. Disk Utility will display a confirmation sheet listing how the volumes will be changed.
    
6. Click the ‘Remove’ button.

Disk Utility will make the changes to the hard drive. Once the volume is removed, you can expand the volume immediately above it by simply dragging its resize corner. For more info, see the ‘Resize Existing Volumes’ topic in this guide.

Published: 7/11/2008

Updated: 1/19/2015

Disk Utility uses the partitioning information you supply to create volumes your Mac can access and use. When the partitioning process is complete, your new volumes should be mounted on the desktop, ready to use.

Before you close Disk Utility, you may want to take a moment to add it to the Dock, to make it easier to access the next time you want to use it.

Keep Disk Utility in the Dock

1. Right-click the Disk Utility icon in the Dock. It looks like a hard drive with a stethoscope on top.
    

1. Select ‘Keep in Dock’ from the pop-up menu.

When you quit Disk Utility, its icon will remain in the Dock, for easy access in the future.

Published: 7/11/2008

Updated: 1/19/2015