Using Disk Utility is one of the effective ways to name a partition easily:
- Go to System > Administration > Disk Utility
- Select the item Hard Disk.
- In the Volumes section, click a partition you want to label.
- Click "Edit Filesystem Label" (See below)
- In the Label box, enter a name, e.g. Data-Disk, and click Apply.
If the option for "Edit Filesystem Label" is not shown, click "Unmount Volume" before hand. In case you can't unmount a volume, try Storage Device Manager to unmount it. See Auto Mount Drives at System Startup.
This tip is for naming a partition using Disk Utility, use other advanced features such as format, edit or delete partition with caution as they can delete data on your disk.