Erasing the contents of the internal SSD in an Apple silicon Mac might seem a simple task, until you consider what’s on it in addition to the user files in its Data volume. Not only is that paired with the System volume, a mounted snapshot, but there are two additional containers that you don’t normally see.

This article explains how you can erase the following:

• the Data volume, shown in blue
• the Boot Volume Group, consisting of the Data and System (pink), and their accessory volumes (green)
• all volumes in the Apple_APFS container (red)
• the entire SSD, including the other two containers (pale yellow).

Assuming that you’re going to install something in their place, it’s up to you to choose, and that will in turn determine how you can install macOS and anything else required to allow your Mac to start up and run again.

Before you try any of these, you should de-authorise that computer in one of Apple’s media apps, and ensure you have a thorough and reliable backup of all the user files.

Data volume

Erase the Data volume by destroying its encryption key using EACAS, Erase All Content and Settings. This doesn’t so much delete anything, as render it inaccessible, so is most economical on SSD use, and quickest without compromising on security. This affects all user accounts with Home folders stored on the internal SSD.

Open System Settings, General, Transfer or Reset, and click Erase All Content and Settings.

If you continue, you should see one final warning before the contents of the Data volume are blown away into the great bit-bucket in the sky.

When that has completed, your Mac will start up for personalisation, configuration, and creation of its new primary admin user, just as it did when it was new. However, it will still be running the same macOS installation as before you used EACAS.

Boot Volume Group

Erase the current Boot Volume Group using Disk Utility in Recovery. Put your Mac into Recovery by starting it up with the Power button held, select Options, select a user and authenticate as that user to display the Recovery window. There select Disk Utility and click Continue.

Select Macintosh HD at the left and click the Erase tool at the top of the window. Enter a name for the volume such as Macintosh HD, select APFS as the format, and click the Erase or Erase Volume Group button.

You might be asked to Erase and Restart, which will lead to a restart and following that your Mac will try to activate over a network.

On completion, quit Disk Utility, select Reinstall macOS if necessary, click Continue and follow the instructions to download and install fresh macOS. Note this procedure doesn’t wipe and reinstall the Preboot or Recovery volumes in the Boot Volume Group.

Some instead select the disk at the top of the list at the left, here named Apple Inc. VirtIO Block Media because it’s running in a VM. In theory that should completely reformat the internal SSD, wiping all three of its containers, and so require a more extensive reinstallation. In many cases, it’s preferable to Restore in DFU mode, to ensure the whole of the firmware is replaced at the same time.

Apple_APFS container

Erase the whole of the Apple_APFS container using Erase Mac in Recovery, which should erase all Boot Volume Groups within that container.

Enter Recovery as normal using the Power button, select Options, and click Continue. Then instead of selecting a known user, use the Erase Mac command in the Recovery Assistant menu. This completely erases all Boot Volume Groups in the Mac’s internal SSD, ready to reinstall macOS, for which it requires an internet connection.

This has the advantage that it can be performed when you don’t know the password to unlock the Data volume (FileVault).

Entire SSD

Erase the entire contents of the internal SSD by formatting it and installing its contents afresh from another Mac, using Restore in DFU mode.

This is described here. Apple has improved that from Sonoma onwards, as it’s no longer necessary to use Apple Configurator 2 on the Mac that’s performing this, but it can all be done in the Finder. To do that, you’ll need another Mac to perform the restore process, and a USB-C data cable to connect the two of them. Don’t try using a Thunderbolt cable, though, as it won’t work. Another secret for success is to plug that cable into the target Mac’s DFU port, that designated to support DFU connections, as detailed here.

Restoring in DFU mode replaces the Mac’s firmware, erases the boot volume group, and installs the bundled version of macOS, leaving that Mac in the same condition in which it was delivered to its first user, with a fresh copy of macOS ready to be personalised and set up. Although that part of the process is fairly quick, full migration is then required before user applications and documents are available. The great advantage of restoring is that you can pick which version of macOS and its firmware are installed.

Which version of macOS will be installed?

When restoring in DFU mode, you can choose which version of macOS will be installed according to the IPSW image you use, making it the method of choice when you intend downgrading that Mac to an older version of macOS.

Methods that obtain new macOS from Apple should install:

• the current version of the most recently installed major version of macOS
• if you have just upgraded macOS, then erased the Boot Volume Group in Recovery, Apple warns that “you may get” the version of macOS that was running before that upgrade.

If you have an Apple silicon Mac, take a look at its Thunderbolt ports and you’ll see that, other than being marked with the Thunderbolt lightning symbol, they all look identical. In fact they’re not: one of them is different from the others, although nothing in or on your Mac will tell you that. One of them is the DFU port, and works differently.

Why two types?

Apple designed these new Macs to provide two important features that depend on how their Thunderbolt ports work:

• the ability to start up in a special Boot ROM mode to allow them to connect to another Mac and have the entire contents of their internal SSD replaced, giving them a new set of firmware and setting them back to factory condition in a Restore process;
• the ability to start up from a bootable external disk while remaining in Full Security mode.

Neither of those is available in Intel Macs with T2 chips.

Because starting up using the Boot ROM alone can only support a plain USB-C and not Thunderbolt connection, that Device Firmware Update or DFU mode uses a Thunderbolt port that also supports DFU. However, as a result that port isn’t able to operate fully with a bootable external disk. Hence, every Apple silicon Mac has one Thunderbolt port designated as its DFU port. That’s used to connect it to another Mac when in DFU mode, but can’t be used to install or update macOS on a bootable external disk.

Apple hasn’t explained how the DFU port is different. My speculation is that the Boot ROM directly runs a simple protocol over USB-C for compactness of code, and to ensure it’s less prone to hacking using malicious devices such as those available for Thunderbolt. In contrast, secure protocols using LocalPolicy to enable starting up from an external system could rely on features that are intentionally blocked for DFU mode. The end result is that, while the DFU port works fine in all other respects, and has full USB4 and Thunderbolt 4/5 support, it can’t be used to make an external disk bootable, nor to update macOS on an external disk that’s already bootable.

Identification

The DFU port appears identical to other USB-C ports and has no marking.

System Information and other utilities in macOS don’t provide any information about DFU ports.

The Mac User Guide provided in the Tips app describes the ports on different Macs without making any mention of the DFU port. It contains no relevant information about creating a bootable external disk (except as a bootable installer), or the use of DFU mode.

Apple has published a support note aiming to identify DFU ports on both Apple silicon and T2 Macs, its current version dating from 4 November 2025. However, the information given in that may not be correct, at least for the MacBook Pro 16-inch 2024. According to Apple, the DFU port on a MacBook Pro 16-inch is “the USB-C port furthest to the left when you’re facing the left-hand side of the Mac”. However, Jeff Johnson has reported the DFU Port on his MacBook Pro M4 Pro 16-inch 2024 appears to be on the right side of its case, not the left.

The original version of that support note appears to have been published on 9 December 2024, four years after the release of the first Apple silicon Macs, and almost seven years after the first Intel Macs with T2 chips. When I discovered it in January 2025, I found it internally inconsistent, “for instance, it shows the DFU port as being that on the left of the left side of a MacBook Pro, but states in the text that on a MacBook Pro 14-inch 2024 with an M4 chip, the DFU port is that on the right of the left side instead.” It has since been updated.

There may be an empirical method of discovering the DFU port using System Information, though. This has been tested on at least a dozen different Apple silicon Macs and has held good so far. In the Hardware section, select the Thunderbolt/USB4 item to list each of its buses. In that list at the top, select Bus 0, and below that you should see its details, including those of the Port, where there will be a Receptacle number, starting from 1. As far as I can tell, Receptacle 1 is normally that for the DFU port.

Having identified which of the buses feeds Receptacle 1, the remaining task is to correlate that with the physical port on your Mac. If you already have a device connected to Receptacle 1, you can identify that from the details given below. On my Mac mini, its backup SSD is connected to Receptacle 1, making it simple to see on the case which is the DFU port.

Use

When connecting an Apple silicon Mac in DFU mode using a USB-C cable, that must be connected to the DFU port on that Mac. If a different port is used, the connection is almost certain to fail.

When connecting an external boot disk to an Apple silicon Mac, for that to work fully as expected, it must be connected to a port other than the DFU port. Although the Mac can still boot from an external disk connected to the DFU port, that can’t be used when installing or updating macOS on the external disk, including when creating it, or in other procedures where LocalPolicy for that disk may need to be created or changed.

Intel Macs with T2 chips

DFU ports aren’t unique to Apple silicon Macs, and are also designated for Intel models with T2 chips. However, their impact is then more limited:

• DFU mode is used more rarely, and only to restore current firmware, rather than perform the full restore process available on Apple silicon Macs;
• external bootable disks don’t rely on LocalPolicy, and are installed and used differently as a result.

Recommendations

• Discover which of your Apple silicon Mac’s Thunderbolt ports is its DFU port.
• Use that port to connect it in DFU mode.
• Use any other port when creating a bootable external disk, installing or updating macOS on it, or performing any operation that might create or change LocalPolicy. When possible, it’s simplest to avoid connecting the disk to the DFU port.
• Apple should check and correct, as necessary, information on the DFU port on the MacBook Pro M4 Pro 16-inch 2024.
• System Information should explicitly identify the DFU port on all Apple silicon Macs.
• Future Macs should identify the DFU port on their case.

You pressed the Power button on your Mac, and nothing happened. It didn’t show signs of starting up, so is it dead, or just pretending? The distinction might seem obvious until you consider DFU mode.

Power reaching the Mac, no sign of life

Simple mains/AC power problems have caught many out: if your Mac isn’t showing any signs of life when it should, ensure that power is reaching it in the first place. Never put yourself at any risk of coming into contact with any live cable, though. Good checks are to verify that the mains socket/receptacle delivers power correctly to another system, and that the Mac’s power cable also does its job. If you’re in any doubt about the electrical safety of either, stop immediately, make everything safe, and obtain professional advice.

If you’re confident that power is going into your Mac, the next and more difficult question is whether the Mac’s hardware is dead, or it has entered DFU mode. DFU mode is the fallback for all Apple silicon Macs that encounter a problem early in the boot process, whether it’s in ROM or later stages before the kernel starts. This also applies to Intel T2 Macs that encounter problems when loading iBridge firmware for their T2 chip, as explained below.

Is it in DFU mode?

Most Apple silicon Macs and T2 models that have entered DFU mode show no obvious signs of life. This is even true of MacBook Pro models with MagSafe 3 power cables: in DFU mode, their LED doesn’t light up. Neither will a notebook keyboard light, nor is there normally any indication that a built-in display has power. Built-in trackpads also feel dead.

Notable exceptions to this are:

• Mac Studio and Mac mini, whose power status indicator light should display amber;
• Mac Pro, whose status indicator light should display amber and may flash.

For all models, once they have connected successfully to a second Mac in DFU mode, you should see the Apple logo and a progress bar on any connected display during IPSW download.

For the Mac Pro, the status indicator light will flash amber in different patterns as a result of memory, PCIe card and other faults. Apple explains those separately for the Mac Pro 2019 and Mac Pro 2023.

DFU mode is detailed by Apple in this support note.

Spontaneously entering DFU mode should be a very rare event, but in most cases the only way to determine whether it has happened is to connect the Mac using an appropriate USB cable to another Mac running recent macOS, which should then connect to the Mac that’s in DFU mode. If that’s suspected, try a firmware Refresh in the first instance to see if that occurs, as that’s non-destructive of the internal SSD’s contents.

Connecting the Macs requires attention to detail. The cable used should be capable of transferring data via USB-C but not Thunderbolt. This is a limitation imposed by DFU mode, and must be observed if the Macs are to connect. That should be connected to the DFU port on the dead Mac, one of its USB-C+Thunderbolt ports. Apple lists those here, and they’re given in MacTracker.

If you aren’t sure, or can’t connect a suitable Mac, it may be best to assume that it’s in DFU mode, and shut it down with a 10 second press of the Power button. On a laptop, DFU mode should use very little power, as there’s normally only one CPU core running and little else. However, as that Mac can’t be charged in DFU mode, this could eventually lead to discharge of the battery.

Not in DFU mode

If there are no signs of life and the Mac isn’t in DFU mode, then it has most probably suffered a fatal hardware failure, and needs the attention of an authorised Apple service provider. If it shows no signs of life in response to a normal press of the Power button, then it’s extremely unlikely to start up in Recovery mode to let you run Diagnostics there.

Signs of life

If the Mac shows signs of life, the next question is how far it proceeds with the boot process:

• It doesn’t reach the login window
• because it freezes and fails to make any further progress, perhaps displaying the Apple logo and progress bar, but no further;
• because it enters a boot loop, in which a kernel panic occurs during boot, forcing the Mac to restart, or to shut down, only to repeat the same sequence.
• It reaches the login window, but sticks there.
• The login window allows user selection and password entry, but refuses any further progress.
• Login is successful, but the Mac freezes or reboots shortly afterwards.
• Login is successful, and problems occur later.

That determines whether you can get it to start up in Recovery mode, and gain access to the tools it provides.

Boot processes

Once a T2 Mac has performed its Power-On Self-Test (POST) and initialised the SMC, the T2 sub-system establishes the level of Secure Boot in force, and, if that’s Full or Medium Security, boot.efi is checked before being loaded, and that leads through to the rest of the boot process. Apple provides a key to the different screens that can appear during these stages.

Boot security in Apple silicon Macs aims to provide a verified chain of trust through each step in the boot process to the loading of macOS, that can’t be exploited by malicious components. Booting an M-series Mac thus starts with the immutable Boot ROM in the hardware, whose most important task is to verify the executable for the next stage, then load and run it. If that isn’t possible, then the fallback is to go into DFU mode and await a connection over USB.

In the event of early boot failure, the only recourse seems to be to abandon the process, and leave the Mac in DFU mode, although Macs running Tahoe could now enter Recovery Assistant to try to fix the problem.