Getting to Know Disk Utility in OS X Yosemite and Earlier
Disk Utility works with disks and volumes. The term “disk” refers to the drive itself. A volume is a formatted section of a disk. Each disk has a minimum of one volume. You can use Disk Utility to create a single volume or multiple volumes on a disk. It’s important to understand the relationship between a disk and its volumes. You can erase a volume without affecting the rest of the disk, but if you erase the disk, then you erase every volume that it contains. Disk Utility has three main sections: a toolbar that spans the top of the Disk Utility workspace, a vertical pane on the left that displays disks and volumes, and a work area on the right where you perform tasks on a selected disk or volume. Disk Utility is located in Applications > Utilities. It’s only located in the Dock while it’s open. If you plan to use Disk Utility for system maintenance purposes or for working with hard drives, add it to the Dock. Click the Disk Utility icon while it is in the Dock and select Keep in Dock.
Erasing a Non-Startup Volume
Erasing a volume is an easy way to free up drive space. Many multimedia applications, such as Adobe Photoshop, need a large amount of contiguous disk space to work efficiently. Erasing a volume is a quicker way of to create that space than using third-party defragmenting tools. Because the process erases all the data on a volume, some multimedia-savvy individuals create small volumes to hold a project’s worth of data and then erase the volume before starting the next project. The data-erase method outlined here doesn’t address any security issues that may be associated with the erased data. Most data recovery programs could resurrect the data that is erased using this process. If you’re concerned about security, use the secure erase procedure addressed later in this guide. To erase a volume: The erased volume retains the same name and format type as the original. If you need to change the format type, see how to format a Mac’s hard drive using Disk Utility later in this guide.
Secure Erase a Volume
Disk Utility provides four options for securely erasing the data on a volume. The options include a basic erase method, a slightly more secure erase method, and two erase methods that meet or exceed U.S. Department of Defense requirements for erasing confidential data from hard drives. If you’re concerned about someone being able to recover the data you’re about to erase, use this secure erase method.
How to Format a Mac’s Hard Drive Using Disk Utility
Formatting a drive is conceptually the same as erasing it. The main difference is that you select a drive, not a volume, from the list of devices. You also select the type of drive format to use. Options for OS X Snow Leopard and Earlier
Don’t Erase Data: This method is quick but not secure. It removes the volume’s catalog directory but leaves the actual data intact. Zero Out Data: This method provides a good level of security. It erases the volume’s data by writing over it with zeros. The length of time this method takes depends on the size of the volume. 7-Pass Erase: This method meets the security requirements of the U.S. Department of Defense’s 5220-22M standards for erasing magnetic media. This erase method can take a long time. 35-Pass Erase: This is the highest level of data erase security that Disk Utility supports. It writes over the data on a volume 35 times. Don’t expect this erase method to finish any time soon.
Options for OS X Lion Through OS X Yosemite The drop-down Secure Erase Options menu presents options similar to the ones in earlier versions of the operating system, but it uses a slider for making choices instead of an options list. The slider options are:
Fastest: This is the quickest erase method. It doesn’t scramble the file data, which means a recovery app may be able to resurrect the erased data.Zero Out the Data: This erase method writes a single path of zeros to all locations on the selected volume or disk. Advanced recovery techniques could restore the data, but it would require a great deal of time and effort.Three-Pass: This is a DOE-compliant three-pass secure erase. It writes two passes of random data to the volume or disk and then writes a single pass of a known data pattern to the volume or disk.Most Secure: This method of securely erasing a volume or disk meets the requirements of the U.S. Department of Defense (DOD) 5220-22M standard for securely erasing magnetic media. The erased volume is written seven times to ensure the data can’t be restored.
This formatting process takes a little longer than the basic erase method.
Erasing or Formatting a Mac’s Startup Drive Using Disk Utility
Disk Utility can’t directly erase or format a startup disk because Disk Utility and all of the system functions it uses are located on that disk. If Disk Utility tried to erase the startup disk, it would, at some point, erase itself, which would present a problem. To get around this, use Disk Utility from a source other than the startup disk. One option is your OS X Install DVD if you have one, which includes Disk Utility. Macs without optical drives use the Recovery volume.
Using Your OS X Install DVD
Using the OS X Recovery HD
Macs that do not have an optical drive boot from the Recovery HD to run Disk Utility. You can then use the steps in the Erase a Non-Startup Volume section early in this article.
