How To Erase Hard Drives

How to Safely Format & Erase your Hard Drive on a Mac

Mac user's are fortunate, as you already have a free application built into Mac OSX for safely erasing a hard drive.  This How-To tutorial will walk you through the whole process with screenshots.

This tutorial assumes that you have (2) Hard Drives.  One that you have booted to, and a 2nd, possibly an external hard drive that you would like to safely erase all your private data from.  A common scenario is that you may have just upgraded your hard drive in your MacBook and now you want to destroy the data on the old one before selling it or passing it to a friend.  If you only have 1 Hard Drive, you can follow approximately the same steps, using the OSX boot CD.

Step 1 - Launch Disk Utility

You can start Disk Utility one of two ways.  Either by opening Spotlight (Command + <Space Bar>) or by going to your applications folder and opening Disk Utility.

Step 2 - Select the Hard Drive you wish to Erase

IMPORTANT: Make sure you select the correct harddrive.  If your hard drive is an external USB Drive, it will usually be indicated by a little orange USB Drive icon.  You'll notice that for each hard drive connected to your computer (internal or external) there are 2 listings per drive.  This is because the top listing refers to the Hard Drive itself, while the sub-listing below is the 'partition' on your hard drive (usually just one).  You can learn more about disk partitioning on wikipedia.

Step 3 - Set your Security Options

After selecting your hard drive, click the 'Erase' tab at the top, after 'First Aid', then click 'Security Options' to open the Hard Drive Secure Erase configuration screen.

The Secure Erase Options screen will pop down.  By default, 'Don't Erase Data' is selected, be sure to change that.  I recommend selecting 7-pass Erase if you have the time.  Be warned, a 500GB Hard Driver on USB2 could take 30 hours to erase at this level !!! 

TIME SAVING TIP: Save time by Selecting 7-Pass Erase and stopping it after the 3rd or 4th pass.  I did this on my last hard drive and cut off 10 hours, yet still had quite a securely erased hard drive.  When you see start on the 4th or 5th pass, hit the 'Stop' button and the process will stopped, but your data will have be overwritten multiple times.

Secure Erase Options
These options specify how to erase the selected disk or volume to prevent disk recover applications from recover it.  Note: Secure Erase overwrites data accessible to Mac OS X.  Certain type of Media may retain data that Disk Utility cannot erase.

• Don't Erase Data (default selection) - This is quick and provides the least security. It erases just the information used to access your files and leave the data in the files unchanged.  Many commonly available disk recovery applications can restore that data.
• Zero Out Data - This is quick and provides good security.  It erases the information used to access your files and writes zeroes over the data once.
• 7-Pass Erase (recommended) - This option takes 7 times longer than "Zero Out Data," and meets the US Department of Defense (DOD) 5220-22 M standard for securely erasing magnetic media.  It erases the information used to access your files and writes over the data 7 times.
• 35-Pass Erase - This option takes 35 times longer than "Zero Out Data" and povides the best security.  It erases the information used to access your files and writes over the data 35 times.

Step 4 - Sit Back, have a beer, or make yourself some Tea

     Photo CC Credit: funkyah

You're hard drive is going to be busy for a while, so you better find something else to distract your time.  Maybe try defragging one of those other hard drives you have lying around the house, just don't follow this guy's advice.