How to fix an external SSD not working on an M-based Mac

Your external SSD isn't showing up on your M-based Mac — and the clock is ticking. I've been there. Here's what actually works, from a quick port check to a full reformat, so you can get your drive back without losing a single file.

Before diving into fixes: It's worth knowing where your Mac stands — if it's still under warranty, Apple may cover a repair. I used this Mac Warranty Check GPT tool to confirm my coverage in under a minute.

Why can't an M-based Mac boot from an external drive?

Macs and Apple silicon chips can’t boot macOS without a working internal SSD. This is due to the new security policy, which completely reimagines the M-based Mac’s boot and recovery process. The policy is based on the so-called 1 True Recovery (1TR) — it’s Apple's security system on Apple silicon Macs that stores startup data on the internal SSD. Without a working internal drive, the Mac can't start at all — even from an external one.

To put it simply, 1TR ensures that your startup's security information is stored internally and written to an internal 1TR partition. Thus, an Apple silicon Mac won’t boot if the internal storage has failed. 

How to make an external SSD work on an M-based Mac

The shift to M-based inevitably caused many incompatibility issues, both with software and hardware. An external hard drive not working on the M-based Mac can be one of the outcomes of such incompatibility. Below, I’ll guide you through a few working methods to make an external SSD work on an M-based Mac.

Here's a quick overview of the main fixes I'll cover in detail below:

Solution	What it does	Time needed
Check System Report	Confirms if Mac detects the drive	30 seconds
Test USB ports	Rules out power/connection issues	2 minutes
Verify encryption	Checks if password protection blocks mounting	1 minute
Run First Aid	Repairs file system errors	5-10 minutes
Update macOS	Fixes compatibility problems	20-30 minutes
Use NTFS driver	Enables Windows-formatted drives	2 minutes
Reformat drive	Last resort to restore functionality	15 minutes

Check if your Mac detects the external driver

This first step will help you determine whether there’s some hardware issue that makes your external drive unmountable, or whether it’s a result of a software problem: 

1. Click the Apple menu, choose About This Mac.
2. Click More Info.
3. In the System Settings window, scroll down and click System Report.
4. Look for your external SSD in the sidebar (under Storage). 

If you can’t locate your external SSD, you’re most likely dealing with a faulty SSD or ports (so basically it’s a hardware issue). If your Mac has recognized the SSD, the SSD itself is fine, but something’s wrong with how that SSD interacts with your system — I recommend checking if the drive is encrypted and making sure to update macOS. 

Check your Mac's USB ports

If your Mac can’t “see” your SSD, check if the ports are okay. Very often, Mac users employ USB adapters and hubs to connect their external devices, and those hubs can cause trouble because external SSDs might need more power to mount on an M-based Mac. Or, your Mac’s own ports might be malfunctioning. 

Here’s what I recommend: 

1. Disconnect your hub/adapter and try connecting the SSD to your Mac’s native port
2. Connect the SSD to a different port
3. Disconnect and reconnect your SSD 
4. If you’re using a self-powered hub, make sure it’s connected to an AC adapter. 

Check if your SSD is encrypted

Depending on the provider of your SSD, there might be encryption enabled by default. So here’s what could happen: your external SSD requires a password to mount on an M-based Mac, but the software that should be used to enter that password is outdated and incompatible with M. As a result, your Mac shows the error saying the SSD can’t be mounted. 

To check if encryption is the issue: 

• Try connecting your SSD to another computer (preferably, an Intel-based one).
• Alternatively, you can try installing a third-party extension to update your SSD software and unlock the external drive on an M-based Mac (look for instructions from the SSD provider).

Run First Aid to repair your SSD on an M-based Mac

Sometimes, it really takes a few minutes to repair your external SSD (mainly, if there’s some kind of file system corruption). First Aid repairs file system corruption on your external SSD in minutes.

To run First Aid:

1. Open Finder > Click in the menu bar Go > Utilities. 
2. Choose Disk Utility.
3. Choose your external SSD and click First Aid. 
4. Click Run to repair the SSD (it might take a few minutes). 

The repair process typically completes within minutes and resolves most file system corruption issues.

Update macOS to the latest version

The fresher your macOS, the fewer compatibility issues you’ll see. So make sure you always keep it updated on M-based Macs.

To update macOS:

1. Go to System Settings > General.
2. Click Software Update > Click Update Now.

Just make sure you have an external bootable backup of your data prepared with Get Backup Pro in advance. 

Recover data, then reformat your SSD

Reformatting a drive requires erasing all data, which can be concerning. But there are ways to protect your data during this process. 

Before reformatting, try making the SSD mountable with iBoysoft NTFS for Mac. It works with SSDs formatted as NTFS — the format that is not natively supported by macOS. iBoysoft enables full read and write support for NTFS drives on Mac, potentially fixing the issue without erasing anything.

Last resort: Reformat your SSD

After you secure your data, you can go ahead and erase your SSD (in case nothing else solves the problem): 

1. With your external SSD connected, access Disk Utility via Spotlight.
2. In Disk Utility, choose the SSD drive from the sidebar 
3. Access the Erase tab. 
4. Select APFS/HFS+ and click Erase. 

This process completely reformats your drive and usually resolves persistent mounting issues.

Can you upgrade the M-based Mac mini's SSD?

Apple doesn’t allow any changes to internal processors, RAM, and SSD on Apple silicon, meaning you can’t upgrade the SSD. 

However, you always have two solutions — you can either use an external SSD to expand storage, or upgrade your internal storage with CleanMyMac, a clutter removal and optimization tool for Mac.

The app lets you quickly scan and delete clutter to clear storage. First, I recommend starting with the Cleanup module to remove system junk and cache, then using the My Clutter module to scan all your folders and remove old, large files and duplicates. This is how I usually scan my Downloads folder (which gets cluttered a lot):

Read also:

• What to Do If Macbook Wont Boot Past Apple Logo
• Fix Time Machine Stuck on Preparing Backup
• Erase Sd Card and Format Usb Drive on Mac
• Factory Reset Mac

How to boot an M-based Mac from an external SSD

For M-based Macs, Apple uses a recovery option called System Recovery. Booting from an external drive still remains the best option, especially if you don’t want to lose your data. 

Here’s how to create a bootable installer for an M-based Mac: 

1. Prepare a native Thunderbolt 3 (or newer) SSD formatted as APFS.
2. Download a macOS installer from the App Store.
3. Save the installer directly to your external SSD (for bootable clones, Get Backup Pro streamlines this process).
4. After your Mac restarts, it boots from the external SSD automatically.
5. Unmount your SSD and switch to the internal drive.

Here’s how to boot your M-based Mac from an external SSD: 

1. Turn off your Mac and connect the bootable drive.
2. Press and hold the power button to turn on your M-based Mac.
3. Select the bootable drive from Startup Options.
4. Your Mac boots from the external SSD.

This process works reliably when you use compatible Thunderbolt drives formatted correctly.

Keep your SSD running smoothly on an M-based Mac

If your external SSD isn't working on an Apple silicon Mac, start with port and encryption checks, run First Aid, update macOS, and use iBoysoft NTFS for Mac if the drive is Windows-formatted. Reformatting is the last resort. Plus, you can always rely on your external SSD, which should work pretty well as long as you follow the recommendations I shared in this article. 

I also recommend getting iBoysoft NTFS for Mac, so you don’t have trouble with incompatible NTFS; CleanMyMac — to optimize your internal storage; and Get Backup Pro — to create a secure bootable clone of your files that will remain available even if your internal drive fails.

Get Backup Pro, iBoysoft NTFS for Mac, iStat Menus, and CleanMyMac are all on Setapp — one subscription, free for 7 days. Get 250+ Apps on Setapp.