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Most Secure: This secure erase option erases the catalog entry and performs a seven-pass write over all data locations. This method meets the DoD 5220.22 M standard for securely erasing magnetic media. Note: OS X Snow Leopard and earlier also offered a 35-pass secure erase option that is quite excessive, and takes a very, very long time to perform. Jul 23, 2016 Choose 7-Pass Erase. Choose 35 if you really want to be sure, but that takes much more time and may be overkill. On the Right Hand Pane, click Erase. This will be your opportunity to install a fresh operating system, if you wish.
In the sheet that appears you’ll see four options—Don’t Erase Data, Zero Out Data, 7-Pass Erase, and 35-Pass Erase. Disk Utility provides a variety of ways to erase your hard drive. Most Secure: This secure erase option erases the catalog entry and performs a seven-pass write over all data locations. This method meets the DoD 5220.22 M standard for securely erasing magnetic media. Note: OS X Snow Leopard and earlier also offered a 35-pass secure erase option that is quite excessive, and takes a very, very long time to perform. Now use the Erase Free Space option, which also offers 1, 3, and 7 passes of erase, and only empties out unused parts of the disk. The advantage is that your computer remains available (though. Once i power it off i can just restart the erase process (single pass this time of course) and then reinstall OS X from the disc at that point?, 07:38 AM #4 Kevriano. Oct 10, 2010 35-Pass Erase— Provides the maximum amount of security offered. This option takes an extremely long time, possibly more than one day. Click the radio button in front of 7-Pass Erase. Click the Erase button next to the Security Options button. Confirm you want to erase.
There may come a time when you want to completely remove all traces of information on your Mac’s drives. It may be because you’re selling or donating your Mac, and you want all your personal information wiped clean from the drive. Or perhaps you want to wipe an older drive that you’re replacing because it’s too small, or because it has started to show a few errors when you test the drive.
No matter the reason, wiping a drive is an easy – though sometimes very long – process that just about any Mac user can take care of on their own.
So, if it’s so easy, why the need for this guide? Well, while the process is simple, there are some important considerations to understand that will affect how you erase your Mac’s drive.
Using Disk Utility to Wipe a Hard Drive
First, we’re going to look at wiping the contents of a hard drive. It doesn’t matter if it’s an internal, external, or your Mac’s startup drive; using these techniques you can obliterate the contents of the selected drive, making it all but impossible to recover the data.
These methods will work for any hard drive you may be using with your Mac. They should not, however, be used with any SSD (Solid State Drive), including a Fusion drive, which contains an SSD element. Don’t worry, though; SSDs can also be wiped, they just require a different technique. We’ll cover SSDs a bit later in this guide.
(Use the slider to select one of four secure erase options.)Erase It and Then Erase It Again
Disk Utility includes a secure erase option that will not only erase the hard drive’s catalog files, which point to where individual files are stored on the drive, but will also overwrite the actual data on the hard drive with new information. Depending on the choices you make in the secure erase options, there may be a single data write pass, or up to 35 passes with various data patterns to ensure that all the original data is scrambled beyond recovery.
Note: There are two versions of Disk Utility commonly in use: OS X Yosemite and earlier, and OS X El Capitan and later. For the most part, the steps in the process are the same for both versions of Disk Utility. The only real difference is the look of the UI. As such, we won’t call out the exact differences, but be aware that what you see in the version of Disk Utility you’re using may not exactly match the images in this guide.
Warning: This process will absolutely remove the data that currently occupies the selected drive. If you need any of the information, make sure you have a backup before proceeding.
Launch Disk Utility, located at /Applications/Utilities/Disk Utility.
In Disk Utility’s sidebar, select a volume or a drive. Selecting a volume will only erase the individual volume or partition you selected. Selecting a drive will erase all volumes and partitions associated with the drive.
Select the Erase tab.
Pick a format type to use. Mac OS Extended (Journaled) is the format normally used with the Mac OS.
Enter a name. You can just leave this entry as is.
Click the Security Options button.
Use the slider to pick the secure erase option you wish to use:
Fastest: This is not a secure erase option and does not overwrite data. This is the default erase method that just erases the catalog entries.
Single Pass of Zeros: Erases the catalog entry plus writes a single pass of zeros to all locations.
3-Pass: This option erases the catalog entry and performs a 3-pass write to all data locations. The first two passes use random data; the third pass uses a known data pattern. This option meets the minimum DOE requirements for securely erasing a drive.
Most Secure: This secure erase option erases the catalog entry and performs a seven-pass write over all data locations. This method meets the DoD 5220.22 M standard for securely erasing magnetic media.
Note: OS X Snow Leopard and earlier also offered a 35-pass secure erase option that is quite excessive, and takes a very, very long time to perform.
Make your selection, and click OK.
Click the Erase button to start the secure erase.
(Selecting a drive will erase all volumes and partitions that were created on the drive.)The time the secure erase will take is dependent on the secure erase option you selected. Selecting the Most Secure option can take a large amount of time, while the Single Pass of Zeros is quite a bit shorter. We recommend the Single Pass of Zeros for any drive that you’ll retain control of, such as in a Mac you’re giving to a family member. The 3-pass option is a better choice when you’ll no longer retain possession of the drive. The Most Secure option is appropriate if you need to meet the DoD requirements, but be prepared for a very long wait.
Secure Erase Startup Drive
If the drive you need to perform a secure erase on is your Mac’s startup drive, you’ll need to first boot from another drive with a Mac system installed, or from the Mac OS Recovery volume.
You can use the instructions in the Everything You Need to Know About OS X Recovery guide to boot from the Recovery HD. Once the Utilities window opens, select Disk Utility, and then follow the instructions above to perform a Secure Erase.
Securely Erasing an SSD or Fusion Drive
SSDs (Solid State Drives) have a vastly different structure than hard drives, and require a different method to securely erase the SSD without causing damage. Using the same secure erase techniques as those used for hard drives can be detrimental to an SSD, decreasing its operating lifetime because of the excessive number of writes involved.
Luckily, securely erasing an SSD is actually easier and faster. Using Disk Utility to perform a simple erase (no secure erase options selected) will result in an SSD that will prove very difficult to recover meaningful data from. Let’s examine why this is true.
(The internal architecture of SSDs makes for a simplified erase process that is also very secure.)SSD Internal Architecture
Speaking in general terms, an SSD has very little in common with a hard drive, other than that they both store data long term. The architecture of an SSD is much more similar to RAM than a hard drive.
SSDs use a map that communicates the logical file location to the computer, but behind the scenes, the SSD may be moving data blocks around in an attempt to ensure all memory cells see the same usage, a process known as wear leveling. The point being that the computer never knows where the actual physical file is located on the SSD, only the logical location provided by the map. The upshot is that once the map has been erased, a computer or an app used to recover data has no way to know the physical location of a file, nor for that matter, anything about the physical structure of the SSD, making any type of recovery by pattern recognition an almost impossible task.
FileVault Can Add Another Level of Security
If you want to go the extra step in securing your data, you can use FileVault to encrypt the data in the SSD before you erase the drive. By using FileVault, all the data on the drive will be encrypted with a 128-bit AES encryption algorithm, and a 256-bit encryption key will be created that can be used to encrypt and decrypt the drive.
Once you use FileVault to encrypt the drive, you can then erase the drive, which will also erase the encryption key, leaving a befuddling array of data scattered about the SSD with no key to decrypt it. What’s left on the SSD will be impossible to reconstruct without the benefit of a large government with very deep pockets, and a whole lot of time on their hands (brute force cracking of 128-bit AES is estimated to take one billion billion years).
Start by using the instructions in the Data Privacy Day: Keep Your Data Safe From Prying Eyes With FileVault guide to encrypt the SSD.
Once the encryption is complete, you can erase the SSD using Disk Utility and the normal erase option.
If you’re erasing your Mac’s startup drive, you’ll need to follow the instructions for booting into the Recovery HD volume, and then use Disk Utility to perform the erase.
Wrap Up
When you need to ensure your data is really gone:
- Use the secure erase options in Disk Utility for hard drives.
- Use the normal erase option for SSDs (with or without pre-seasoning with FileVault).
- For those who want to go the extra mile, a sledgehammer may be a handy tool.
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Securely wiping a drive, removing all of its data, and ensuring that no meaningful information can be recovered, has long been a feature of Disk Utility and its erase function. Even though the default for Disk Utility is a simple erase, a secure wipe was just a few clicks away.
Two recent changes have made the traditional secure wipe, performed by overwriting a volume multiple times with various types of data patterns, largely a thing of the past. The first change, leading to less reliance on the various secure wipe options, has been the proliferation of SSDs, both as original equipment provided by Apple and by resellers, such as OWC, which bring higher performance storage systems to the Mac.
(Using the Security Options to sanitize a volume may be a thing of the past.)The second change that directly affects the Mac community, at least in the way free space can be securely erased, is the release of the APFS file system, and how it makes use of shared space between multiple volumes.
In this guide, we’re going to look at erasing volumes, partitions, and containers. We’ll be looking at drives formatted with APFS as well as those formatted with the traditional HFS+ file system. If you’re working with macOS Sierra or earlier, you may find the Rocket Yard Guide: How to Use Mac’s Disk Utility to Securely Wipe a Drive a good source of information for erasing your drives.
We’ll be using the Disk Utility app included with macOS High Sierra and later.
Erasing a Volume: The Basics
Let’s start off with erasing a volume to casually remove any stored data on the selected volume. In this case, we just want to free up the space for a new use, and aren’t worried about anyone being able to recover any of our old data.
Launch Disk Utility, located in the /Applications/Utilities folder.
Select View, Show All Devices, or click the View button in the Disk Utility toolbar, and select Show All Devices from the popup menu.
In macOS High Sierra and later, volumes can be carved out of the drive using partitions, or if the drive is formatted with APFS, they can be part of a container. By setting the sidebar to Show All Devices, we can readily see what a volume is associated with. This can affect the way we might choose to erase a volume.
(Make sure the volume you wish to erase is selected, then use the Erase button in the toolbar to begin the erase process.)In the sidebar, select the volume you wish to erase. The volume is the lowest item in a drive’s hierarchical view. You should see “Physical Drive, Volume” for HFS+ formatted drives, or “Physical Drive, Container, Volume” for APFS formatted drives.
With the volume you wish to erase selected, click on the Erase button in the Disk Utility toolbar, or select Erase from the Edit menu.
The Erase sheet will drop down, presenting the options to change the volume’s name and format, and whether to use any of the Security Options. In this example, we’re just performing a simple erase, so leave everything as is, except for changing the name, if needed, and then click the Erase button.
The erase sheet will change to display a progress bar. When the erase has finished, click the Done button.
Erasing a Hard Drive Volume with Security Options
If you wish to erase a hard drive’s volume and ensure the old information it contained can’t be easily recovered, you can use the Security Options offered when choosing the erase function.
But before you make use of the Security Options, make sure the volume being erased is part of a hard drive and not a fusion drive or an SSD. The security options can shorten the life of SSDs by causing excessive writes to the SSD to occur. In the case of SSDs, for all but the most advanced security needs, you don’t need to use any of the multiple write security options to prevent old information from being recoverable.
(The Erase Security Options feature lets you pick the number of write passes that are made on the selected volume.)
If the volume you wish to erase is part of a hard drive, follow the steps outlined in Erasing a Volume: The Basics, above, until the erase sheet is shown. At this point, click the Security Options button.
The Security Options sheet will be displayed, showing a slider you can use to select one of four methods to erase the selected drive. The Fastest method is the same as the standard erase, and performs no special function to ensure any level of security. Picking this option will result in the volume being erased, but data can be recovered with basic data recovery apps.
Moving the slider one click towards the right will produce the first secure erase, which writes a pass of random data followed by a pass of all zeros across the selected volume. This two-pass write method will keep most individuals with prying eyes using conventional data recovery techniques from being able to access your old information.
The next security option produces a DOE-compliant three-pass secure erase. It uses two passes of random data followed by a third pass using a predefined data pattern. Using this method should secure your old data against most individuals, businesses, and governments not willing to spend excess money or time to uncover your data.
The last and most secure option is a seven-pass erasure that meets DOD 5220-22M standards for a secure wipe of magnetic media.
As you advance the slider to more secure options, you also substantially increase the time it takes to perform the erase. Make sure you really need this level of security before proceeding.
Make your selection and click the OK button, then click the OK button to begin the actual erase.
Securely Erasing SSDs and APFS Volumes
Unless you need to meet a specific business or government requirement, SSDs don’t need to use the secure erase options listed above. By their physical nature, SSDs are inherently secure after a basic erase process. The reason for this has to do with the internal architecture, logical to physical cell mapping, and wear leveling. Once the logical to physical map is removed, which occurs during a standard erase, accessing the internal data would just produce a hodge-podge of data that would be nearly impossible to decipher. You can read more about this in How to Use Mac’s Disk Utility to Securely Wipe a Drive.
If you’re really worried about old information on your SSD being recoverable, and you don’t think the inherent security offered by how an SSD works is enough, you can use this next method to produce an enhanced secure erase.
(Erasing a volume by changing the format to include encryption, followed up by a second standard erase, will create a nicely sanitized volume with little chance of data recovery.)A better and much faster method to produce a sanitized SSD volume is to encrypt the data on the drive, and then erase it, removing the stored encryption key along with everything else. Since encrypting the volume will make use of 128-bit encryption and use a 256-bit encryption key, it’s estimated it would take one billion years using brute force to break the encryption. Of course, it’s also possible that the first brute force attempt could break the encryption, but it isn’t very likely.
Discover more about setting up and using encryption in the Rocket Yard Guide: Data Privacy Day: Keep Your Data Safe From Prying Eyes with FileVault.
If you’re using an APFS volume or an HFS+ volume, you can use the optional encryption format, available when you erase a drive. Simply follow the steps in Erase a Volume: The Basics, above, and when the Erase sheet appears, change the format drop-down menu to APFS (Encrypted), or Mac OS Extended (Journaled, Encrypted).
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You can also encrypt a volume by right-clicking on the volume on the Desktop or in a Finder window and selecting Encrypt “Volume Name” from the popup menu.
Erasing APFS Containers
APFS volumes share the space within a container. This space sharing has a number of advantages, letting your volumes grow and shrink automatically as needed. But it could also have a security disadvantage. The shared space area of a container could hold old file data, even though the volume that originally contained the information was deleted.
If the container uses APFS encryption or the APFS formatted drive is an SSD, this should not be a concern. In the case of an SSD, the logical to physical map detailing the location of any old file was removed when the volume was deleted. And if the volume was using encryption, the encryption key was lost when the volume was removed.
Even so, some of you will want to be doubly, or even triply, sure, and erase the container when a volume is also deleted.
Note: This process is only valid when a container houses multiple volumes and the physical drive contains multiple containers. If you have a container with only a single volume there’s no need to remove the container.
(Use the minus (-) button to remove a container.)
To erase a container, select the container from the Disk Utility sidebar.
With the container selected, click the Partition button in the toolbar.
A sheet will drop down, asking if you wish to partition or add a volume. Click the Partition button.
A pie chart will appear, displaying any container or partitions on the physical drive. Make sure the container you wish to remove is selected in the pie chart.
Warning: The next steps will erase data from the selected item.
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Click the minus (-) button to have all volumes housed within the container, as well as the container itself, removed. The pie chart will be updated to show the outcome. If this is what you intended, click the Apply button; otherwise, click the Revert button to leave the drive untouched.
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Wiping a Volume, Container, or Drive: Troubleshooting
One of the more common problems you may encounter is the failure of an erase or a secure erase process to finish. In most cases, the problem occurs when the targeted volume or container fails to unmount. This can occur because one or more files is in active use. Close all open apps, including Disk Utility, then relaunch Disk Utility and try again.
If you still have an unmount failure, you can try manually unmounting the volume by selecting the volume in the Disk Utility sidebar, and then select Unmount from the Edit menu.
Another common problem is the inability to delete a container. This problem can arise when a container houses multiple volumes. Normally, deleting a container should force all volumes within the container to be removed, and then the container to be deleted. If a volume should fail to be removed, the container delete process will quit with an error. Try deleting each volume within the container by right-clicking the volume in the sidebar and selecting Remove Volume from the popup menu. Repeat for each volume within the container.
You can also run into an issue if the container you wish to delete is the first container on a drive. APFS drives require at least one container. Instead, perform an erase on the physical drive (Warning: All data on the drive will be lost).
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