Fixed: The Disk You Attached Was Not Readable by This Computer (on Mac)

Users tend to store essential files or data in an external hard drive or USB flash drive in case of computer crashing and data loss. Unfortunately, some people reported that they encountered the warning that “the disk you attached was not readable by this computer” when they tried to plug an external drive into a Mac computer.

the disk you inserted was not readable by this computer

You fail to access the folder but eject or initialize the external disk drive due to the unreadable risk. According to user reports, the error that “the disk you inserted was not readable by this computer” occurs to various macOS versions such as macOS Catalina, Mojave, High Sierra, and Monterey.

On macOS Big Sur, the error message is slightly different and turns to “the disk you attached was not readable by this computer”.

Are you worrying that your important data will be lost? Don’t worry! This article will walk you through a comprehensive fix to get rid of the “disk not readable” issue on MacBook Air or Pro.

Why Was the Disk You Attached Not Readable by This Computer?

When your inserted disk wasn’t readable by this computer, it reflects that there are problems with the external disk, SD card, USB flash drive, or the macOS hardware. Specifically, common causes of the unreadable disk are:

The disk goes corrupted;

Mac hardware runs into problems, so your computer can’t read the external hard drive;

The file system like the NTFS drive read doesn’t work well on your Mac;

The format of the disk is incompatible with macOS;

You have forcibly shut down the Mac computer.

How to Fix “The Disk You Attached Was Not Readable by This Computer” on Mac?

If you are to get the external disk drive or USB flash drive or SD card to be read by the Mac computer, you need to troubleshoot possible problems with the disk and the components on Mac related to the disk. Just follow the solutions below one by one until you find out what causes your external disk driver not to be readable and fix it.


Solution 1: Check the Disk Hardware and USB Port

If the external disk drive or USB flash drive or the disk hardware is problematic, odds are that you will encounter “the disk you attached wasn’t readable by this computer”. In this way, you would better check issues with the disk hardware.

1. Insert or attach another USB flash drive or external hard drive or SD card to check whether it is readable on your Mac. If the newly inserted disk can be read by the macOS, it implies that the previous disk hardware is corrupted or damaged, and you may need to replace a new one;

2. Insert the disk to the USB port on another computer. If the external disk works on another device, it means that the USB port or the lightning cable doesn’t work;

3. Insert the disk again and check whether the Mac prompts you to enter a password to unlock the encrypted disk. Sometimes, if the external hard drive is encrypted, the Mac computer can’t read the disk.

If you find that another external disk drive doesn’t work on the Mac, either, it means that the hardware on your device goes wrong, so you need to reset the SMC to fix the hardware issues on the Mac.

Solution 2: Check the File System Format

The file system format of your USB flash drive, external hard drive, and SD card will also cause a “disk not readable” error.

Normally, Windows PCs support NTFS format, while Mac computers support Hierarchical File System Plus (HFS+). If the file system format of the disk is NTFS, it is likely that your Mac computer cannot read the disk.

In this way, if the error that “the disk you attached was not readable by this computer” results from the unsupported file format, you may have to transform the format of the disk. However, disk formatting may cause data loss, so you may as well back up the data in advance.

Solution 3: Repair the Disk with Disk Utility

Now that the disk you inserted was not readable by the Mac computer, you can just repair the disk with the Disk Utility within the macOS.

It may help you check and repair errors related to the file system format of the Mac disk, thus fixing disk permission errors on your Mac. Do not worry. Disk Utility First Aid won’t erase data on your disk drive.

1. Open Launchpad, and then search for Disk Utility in the search box.

2. In Disk Utility, on the left pane, locate and right-click the disk to Run First Aid.

run first aid in disk utility

3. You can see Disk Utility is Running First Aid to check disk permission issues.

running first aid

4. After the process, restart your Mac and then insert your external hard drive or USB flash drive into the Mac.

Some users reported that “First Aid” failed, and Disk Utility can’t repair the disk. In this case, you can try to repair the external disk or storage again to check whether the disk you attached is still not readable.

Solution 4: Initialize the Disk

If Disk Utility doesn’t work to fix the unreadable disk issue, you may have to initialize the disk. so that you can use this flash drive or disk in the future. However, initializing the disk may get rid of all the data and files, so you may as well recover the data in Solution 5.

1. In the warning, click Initialize.

2. In Disk Utility, on the left pane, select the disk drive.

3. Hit Erase, and then confirm to format the disk.

After that, you can re-attach the external storage or USB flash drive or SD disk to see whether it is readable on the Mac computer.

Solution 5: Repair and Protect the Disk with Data Recovery

If you have initiated or formatted the external hard drive or USB flash drive, chances are that your data has been lost.

In this case, Data Recovery for Mac, a professional tool that recovers deleted or lost files such as documents, photos, audio, videos, emails, and so on due to the hard drive issue, accidental deletion, or computer crashes, will be a great helper.

Whether you wish to resolve the unreadable disk error or recover data when you have carelessly deleted data, you can make full use of this tool to fix the external disk issue.

1. Download, install and run Mac Data Recovery.

2. Choose the lost data type and the disk drive, and then Scan deleted files.

data recovery choose file type and lost data location to scan

As you can see, you can recover file types like Image, Audio, Video, Email, Document, Hard Disk Drivers, and Removable Drives.

3. Find and check the lost files, and then hit Recover to get the files back to your Mac.

recover lost data in data recovery

You can now see the deleted files in the unreadable disk. In this way, even if you tried to initialize the disk, you can recover the lost data in the external disk drive or SD card, or USB flash drive with the help of the professional tool.

Solution 6: Update the macOS

The outdated macOS may fail to read your external storage or memory card, so you might as well update the Mac operating system. Sometimes, the latest macOS may bring improved features and applications, and the disk you attached to the Mac may be readable.


If you run into the problem that “the disk you attached was not readable by this computer”, you can try solutions in this tutorial to get the Mac computer to read the files.

Brian Peng
Brian Peng is a PC technician and network engineer with over 13 years of IT experience. He has worked in the IT industry for a long time, providing IT support and network service support for various companies. Currently, he has written over 1000 articles about computers, games, and mobile.

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