I recently needed to format an external 5TB Seagate Backup+ Desk Media USB hard drive.So, I decided to use the Disk Utility application, which is included in Mac OS X. This post describes the how to erase and format a USB Drive on Mac OS X and also addresses a particular error scenario I encountered:
Connect the External USB Hard Drive or USB Storage Device
Plug-in the USB storage device and let Mac OS X mount it automatically. As a result, the device will appear as an icon on the desktop as shown below. Here, I have connected a Seagate 5TB external USB hard drive, which I want to erase and format.
If the device can not be mounted, it may be currently formatted using a file system format that is not supported by Mac OS X or the drive can not be read for some other reason. In this case, you can continue by launching the Mac OS X Disk Utility application.
Use the Mac OS X Disk Utility Application to Erase and Format USB Device
Press F4 to open the Mac OS X Launchpad and use the search bar to find the Disk Utility application. Click on its icon to start it.
In the Disk Utility application, select the hard drive that you want to erase and format. Please note that all data on that drive will be permanently deleted once you start the erase and format process.
If your hard drive does not show up by its name in the left-hand side list as shown above and you select a disk instead when clicking on Erase, you may get an error as shown in the following screen shot:
When clicking on Show Details, an error, saying that there is not enough space on the device, or similar, may be shown:
Use the list view icon in the upper right-hand corner of the Disk Utility application and switch the view to Show All Devices.
The external USB storage device should now be listed by its name, select it and click on Erase to continue.A new dialog will appear. It allows you to enter a name for the external USB drive and to select a format. Leave the Scheme to GUID Partition Map, unless you specifically need a different one or want to make the drive bootable.
Security Options
Click on Security Options… to change the default settings. By default, the drive will be erased using the fasted, most unsecure method. The data can be recovered quite easily using disk recovery applications. If you plan to sell this drive or need to permanently delete sensitive data, make sure to use a more secure erase method.
The Security Options dialog provides four options, ranging from Fastest to Most Secure:
Security Option 1 (Fastest) – This option does not securely erase the files on the disk. A disk recovery application may be able to recover the files.
Security Option 2 – This option writes a pass of random data, and then a single pass of zeros over the entire disk. It erases the information used to access your files and writes over the data two times.
Security Option 3 – This option is a DOE-compliant 3-pass secure erase. It writes 2 passes of random data followed by a single pass of known data over the entire disk. It erases the information used to access your files and writes over the data 3 times.
Security Option 4 (Most Secure) – This option 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.
Erase and Format Process
Select a security option and click on OK and then on Erase to start the erase and format process. Depending on the selected security options and on the size of the storage device, the erase and format process may take a few minutes, several hours or several days.
In my case, where I erased a 5TB Seagate Backup+ Desk Media, the process took about 3 to 4 hours. Once the erase process is completed, the Disk Utility will show a success message. Click on Done to close the overlay.
The USB storage drive is now ready for use and will be automatically mounted by Mac OS X. The Disk Utility shows details about the storage device. Here, 1.31GB are used by the file system and nearly 5TB are now available.
