Erasing Drives with Disk Utility

Danger, Will Robinson! Danger!" That's right, Robot, it is indeed very easy to erase your Mac's hard drives without meaning to. To paraphrase the rules for handling a firearm responsibly: Never click this button unless you mean to use it.

Mac OS X's Disk Utility is where you find the tools to erase disks. You need only erase a disk or volume when you want to completely erase the contents of that existing disk or volume. You can also erase a rewriteable CD (CD-RW) or DVD (DVD-RW, DVD+RW, or DVD-RAM) with Disk Utility.

Erasing an entire disk deletes all volumes on the disk and creates a single, new empty volume.
Erasing a volume only wipes out the contents of that specific volume, leaving all other volumes on the physical disk untouched.
You cannot erase the startup disk — that is, the disk on which Mac OS X is installed and your Mac is booted from. To erase your startup disk, you must startup with the Mac OS X Installation CD and use its Disk Utility.
To erase a disk or volume, follow these steps:

1.From the Erase panel within Disk Utility, click the disk or volume icon that you want to erase from the list on the left side.

2.Click the format that you want to use from the Volume Format drop-down list.

Always choose Mac OS Extended unless you have a specific reason to use the MS-DOS File System or the UNIX File System.

3.In the Name field, type the name of the new volume.

4.If you're erasing a disk, enable the Install Mac OS 9 Disk Driver check box.

5.Click the Erase button.

6.In the confirmation dialog box, click Erase to confirm that you do actually want to do this.

Check, double-check, and triple-check to make sure you're erasing the correct disk (especially if you have multiple FireWire disks plugged into your Mac). In fact, you may want to unmount the disks you know you don't want to erase just to make sure you don't pick the wrong disk! And don't forget back up all the data from the disk beforehand, if necessary