How to Initialize or Erase a New or Existing Drive

When a new drive is attached or installed, OS X will prompt you to do something about it for each such uninitialized drive, as shown below.

Clicking Initialize… brings up Apple Disk Utility. It won’t do anything harmful on its own; it launches Apple DiskUtility where the choices are open.

An uninitialized disk has appeared (Apple OS X)

Erasing

Select the new drive at left, in this case 4TB HGST HDS..., then click on the Erase tab (between First Aid and Partition).

Choose a name (Master as shown here), then click the Erase… button. This creates a single volume; for more than one volume, the drive should be partitioned.

Erasing a drive to a single new volume

Volume “Master” on Desktop

Confirming

After clicking the Erase… button, a confirmation dialog is presented. To proceed, click Erase. When done, the volume will appear on the Desktop with the chosen name (assuming the Show these items preference is selected in the Finder).

If this is a backup drive, it is generally a good idea to exclude it from Spotlight search.

Confirming erasure of a drive