How to Use macOS Disk Utility to Securely Erase External Drives

When you delete a file on a Mac and empty the Trash, the file isn’t actually destroyed. macOS simply deletes the pointer to that file in the filesystem index, telling the computer that the space is now available to be overwritten. Until new data is saved directly over that exact physical spot on the drive, the original file can be recovered using basic forensic software. If you are selling an old external hard drive, returning a company laptop, or destroying sensitive financial records, a simple reformat is not enough. You must use macOS Disk Utility to securely wipe the drive.

Understanding SSDs vs. Mechanical Hard Drives

Before proceeding, it is critical to understand the type of drive you are erasing.

• Modern SSDs (Solid State Drives) and Apple Silicon Macs: You cannot use the traditional multi-pass secure erase method on these drives. SSDs use complex wear-leveling algorithms that scatter data invisibly. Attempting a multi-pass overwrite will just damage the lifespan of the SSD without guaranteeing the data is gone. Instead, modern Macs use hardware encryption. When you “Erase” an APFS-encrypted SSD, macOS instantly destroys the cryptographic key. The data remains on the chips, but it is mathematically impossible to decrypt, rendering it permanently unreadable in a fraction of a second.
• Mechanical HDDs (Hard Disk Drives) and USB Flash Drives: These older, spinning platter drives (or cheap thumb drives) do not have hardware encryption. To guarantee data destruction, you must physically overwrite the entire drive with zeroes or random data.

Step 1: Open Disk Utility

1. Plug in the external drive you wish to erase.
2. Press Command + Space to open Spotlight Search.
3. Type Disk Utility and press Return.
4. In the Disk Utility sidebar, click View and select Show All Devices. This ensures you are erasing the root physical drive, not just a logical volume on it.

Step 2: Select the Drive and Choose Security Options

1. In the left sidebar, click on the root level of your external drive (e.g., “WD Elements Media”).
2. Click the Erase button at the top of the window.
3. A dialog box will appear. Before clicking Erase, click the Security Options… button. (Note: If this button is grayed out, you are either selecting an SSD or the internal startup disk, which do not support this feature).

Step 3: Choose the Erasure Level

A slider will appear with several options, ranging from Fastest to Most Secure.

• Fastest (Level 1): This is a standard quick format. It only removes the directory information. Data is easily recoverable.
• Level 2 (2 Passes): This writes a single pass of random data over the entire drive, followed by a single pass of zeroes. This is sufficient for almost all personal or standard business use cases and thwarts all commercial recovery software.
• Level 3 (3 Passes): This is a DOE-compliant (Department of Energy) secure erase. It writes two passes of random data and one pass of known data. It takes significantly longer.
• Most Secure (7 Passes): This meets the incredibly strict US Department of Defense (DoD 5220-22 M) standard. It overwrites the entire drive seven times. Warning: Running a 7-pass wipe on a 4TB mechanical hard drive can take several days to complete.

Step 4: Execute the Wipe

1. Drag the slider to your desired security level (Level 2 is recommended for most users) and click OK.
2. Give the drive a new Name.
3. Choose a Format (APFS for Mac-only, ExFAT for Mac and Windows compatibility).
4. Click Erase.

Disk Utility will begin the arduous process of writing data to every single sector on the disk. Do not unplug the drive or put the Mac to sleep until the process is completely finished.