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
- Launch Disk Utility, located at /Applications/Utilities/.
- 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.
- Select the hard drive associated with the volume you wish to expand.
- Click the ‘Partition’ tab.
- Select the existing volume that you wish to split into two volumes.
- Click the ‘+’ (plus or add) button.
- 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.
- Disk Utility will dynamically display the resulting Volume Scheme, showing how the volumes will be configured once you apply the changes.
- To reject the changes, click the ‘Revert’ button.
- To accept the changes and re-partition the hard drive, click the ‘Apply’ button.
- Disk Utility will display a confirmation sheet that lists how the volumes will be changed.
- Click the ‘Partition’ button.