Solutions to Fix "The Disk You Inserted was not Readable by This Computer"

By Katrina | Posted to Home > Mac Data Recovery Tips, updated on December 15th, 2020 |

Summary: Errors "The disk you inserted was not unreadable by this computer" pops up on High Sierra/Mojave/Catalina. And in macOS Big Sur, it's '"the disk you attached was not readable by this computer." In this guide, you will learn how to fix it and then recover lost data from unreadable HDD, USB, flash drives, and SD cards with iBoysoft Data Recovery for Mac.

When you connected a USB drive, a flash drive, an SD card or an external hard drive (HDD) to your Mac computer, you may be prompted with an error message "The disk you inserted was not readable by this computer".

In macOS 11 Big Sur, the error message is "The disk you attached was not readable by this computer."

If the Mac is running Mac OS X or earlier, the error message should be "The disk is unreadable by this computer. Do you want to initialize the disk on Mac?"

In this article, we will walk you through the reasons of and solutions to fix this error on macOS Big Sur/Catalina/Mojave/High Sierra and earlier.

The disk you inserted was not readable by this computer.

The solutions to "The Disk You Inserted was not Readable by This Computer" error:

Please keep in mind: DO NOT HIT Initialize... if you won't want to lose files stored on the external drives.

Now, let's dive into details.

1. What Cause the Disk to be Unreadable on Mac?

Generally speaking, the main reason leading to "The disk you inserted was not readable by this computer" error is because, the operating system is unable to read the data on the disk in an orderly fashion, or even not able to access the disk at all.

The possible factors could be:

  1. Disk failure. It's possible that either the disk itself (such as having bad sectors) or the USB interface has suffered some unexpected damages, especially after the disk has been plugged and unplugged frequently.
  2. Corrupted partition table or file system. The operating system must rely on the partition table, file system and other partition information to understand how does the disk organize data. Once such information is corrupted, the operating system will fail to access the disk. In Windows, it's usually known as RAW file system.
  3. The disk is encrypted. For example, if the disk is encrypted by Windows BitLocker Drive Encryption, you'll see this error message too.
  4. The disk is a brand-new one. This disk being unreadable error can also occur if the disk you've inserted is a brand-new one, which has not been assigned with partition information. It is also known as uninitialized.
  5. Improper operations or sudden power off. For example, the disk has been removed abruptly, the computer has been force restarted, or it has experienced sudden power off. These will result in connection issues.
  6. Virus attacks. If the disk has been attacked by virus, the structure data of the disk must be re-written therefore become unreadable to the operating system.

This error occurs frequently on external storage devices. It could be an unreadable Seagate external hard drive, an unreadable WD My Passport, an unreadable Toshiba external hard drive, an unreadable SD card, etc.

No matter what made your disk unreadable on your Mac, you can follow the solutions in the next part to fix this error without worrying about data loss.

2. Solutions to "The Disk You Inserted was not Readable by This Computer"

These solutions can be utilized to fix unreadable external hard drives, USB drives, flash drives, SD card and other storage devices on macOS Big Sur/Catalina/Mojave/High Sierra. Just try them out one by one until you can access the disk again.

Solution 1: Do some basic checks

As aforementioned, there could be connection issues between your disk and the Mac computer, including MacBook Pro, MacBook Air, iMac or other. So, before you start to fix the unreadable disk, you can follow the simple steps here to eliminate some external possibilities that caused "The disk you inserted was not readable by this computer" error.

  • 1. Re-insert your unreadable disk. Safely unplug the unreadable disk and then re-insert it. Sometimes, magic will happen.
  • 2. Insert the unreadable disk to a different USB port, or change a USB cable. At times, it's just the issue of the USB port or USB cable. So, just try another one.
  • 3. Insert the unreadable disk to another computer, either a Windows PC or a Mac. If the computer is still not reading the inserted disk, there is probably something wrong with it.

In the event that the disk is still inaccessible after you have done these checks, you can move on to the next solution.

Solution 2: Check if the drive is encrypted

The process of encryption is to turn the plain texts (the files stored in the disk) to cipher texts. The encrypted data is unreadable unless you can decrypt it with the password. When you insert a disk encrypted with Windows BitLocker Drive Encryption to Mac, the error message "The disk you inserted was not readable by this computer" will also pop out. That's because, Apple doesn't support this Windows drive encryption technology.

How to open BitLocker encrypted disks on Mac?

Though Apple doesn't natively support BitLocker encryption, you can take advantage of a BitLocker for Mac driver to open, read and write to the disk seamlessly on Mac.

Solution 3: Fix the unreadable disk with First Aid

First Aid, a built-in tool in Mac Disk Utility, is designed to verify and repair disk errors, especially the errors with file systems. As mentioned above, the reason leading to "The disk you inserted was not readable by this computer" error could be the file system corruption. So, if First Aid is able to repair the corrupted file system of the disk, your Mac computer could be able to read the inserted disk again.

How to repair an unreadable disk with First Aid?

  • 1. Go to Applications > Utilities, click Disk Utility to launch it.
  • 2. Select the unreadable disk in the left side bar.
  • 3. Click First Aid tab on the top of Disk Utility window.
  • 4. A window will pop up and ask whether you'd like to run "First Aid" on this disk. Click Run to continue. It could take some minutes to complete the process.

Fix unreadable disk with First Aid

If Disk Utility reports that the disk appears to be OK or has been repaired, click Done to quit it. Then, you can safely eject your disk and plug it into your Mac again. Probably, you can open the disk and access files on it without problems.

However, if it reports First Aid failed to repair this disk, you need to reformat or initialize the disk, as mentioned in solution 4.

First Aid failed to fix unreadable disks

Solution 4: Initialize the unreadable disk on Mac

Technically, at the very beginning of partitioned disk, there's a sector called MBR (Master Boot Record) which holds on the information on how the logical partitions, including file systems, are organized on that disk.

For a brand-new disk, users need to assign such information to the disk so that the operating system can access it correctly. For a used disk (has data stored on it already), if the disk becomes inaccessible due to MBR corruption, users need to rebuild the MBR. The process of (re)build MBR is called disk initialization.

Typically, disk initializing will re-partition or reformat the disk to fix the unknown logical errors, which will erase data on the disk.

That's why this solution can be applied only if:

  1. this disk is a brand-new one;
  2. or you have a backup copy of this used disk.

How to initialize the unreadable disk?

Note: If you have important data on this disk, DO NOT INITIALIZE the disk directly. Instead, you need to at first recover lost data from the unreadable disk.

  • 1. Go to Applications > Utilities > Disk Utility.
  • Alternatively, you can also eject the unreadable disk and reinsert it again. Then, click Initialize... button to launch Disk Utility.
  • 2. Select the unreadable disk in the left side bar.
  • If you can't see the disk from the side bar, click View from the upper left menu bar and select Show All Devices from the drop-down menu. The disk will show up in the side bar.
  • 3. Click on the Erase button on the top of the Disk Utility window.
  • 4. Enter the asked info (name, format, etc.) and then click the Erase button.

After the formatting process completes, the disk has been assigned with a recognizable file system. Therefore, the disk is probably readable again on Mac now.

3. Recover Data from Unreadable Disks on Mac

If you have tried out all the solutions above, especially after Disk Utility has failed repairing the disk, it indicates that there might be some severe errors on the disk, such as bad sectors. In that case, recovering data from the unreadable disk is the last solution to let you re-gain access to files.

iBoysoft Data Recovery for Mac - the best external disk data recovery software

iBoysoft Data Recovery Software for Mac is one of the best Mac data recovery software that is able to recover lost data from unreadable hard disks, USB disks, flash disks, SD cards, memory cards and much more storage devices. With it, you can easily regain access to photos, videos, documents, email and music files on the disk. Besides, it supports recover files from disks formatted with APFS, HFSX, HFS, HFS+, exFAT and FAT32 file systems.

Tutorial to recover lost data from unreadable disks with iBoysoft Data Recovery for Mac

  • 1. Download, install and launch iBoysoft Data Recovery for Mac.
  • It is able to list all detected external disks, as well as internal disks, on its main interface. You will also find all recognized partitions on each disk.
  • 2. Select the unreadable disk from the main interface.
  • iBoysoft Data Recovery for Mac Select
  • 3. Click Scan.

iBoysoft Data Recovery for Mac supports two scanning modes: Quick scan and Deep scan. With the built-in advanced algorithm, it will run the best scan mode automatically according to your disk's situation.

The scanning process should take a while. After the process finished, you can click the Camera icon to save a session file. It will be especially helpful if there're bad sectors in the disk.

iBoysoft Data Recovery for Mac Scan

  • 4. Click the search results to preview and evaluate which file to recover.
  • This data recovery software for Mac supports a bunch of file types to preview, including pictures, videos, documents and audio.
  • iBoysoft Data Recovery for Mac Preview
  • 5. Choose the files you want, click Recover button. Please specify a different location to store the recovered files.

iBoysoft Data Recovery for Mac Recover

In addition to recovering data from unreadable disks, iBoysoft Data Recovery for Mac can also recover lost data from corrupted external drives, and also from formatted or unmountable drives on macOS Big Sur 11/10.15/10.14/10.13/10.12 and OS X 10.11/10.10/10.9/10.8/10.7.

If none of the solutions above fixed the unreadable disk, it's very likely that the disk has been damaged physically. You need to send it to repair or to buy a new one.

Tips to Avoid Disks Becoming Unreadable on Mac

As the saying goes: Prevention is better than cure. To avoid "The disk you inserted was not readable by this computer" error, the following tips should be helpful.

  1. Eject the drive safely every time you finish using it on a computer.
  2. Disconnect your drive first if you are going to turn off the computer or restart it.
  3. Be sure to shut down your Mac computer before the battery wears out
  4. Handle the drive with carefulness. Don't drop it hard or bounce it around, which can cause damage to the USB port, USB cable as well as the drive itself.
  5. Back up your important photo files, video files, documents and other important files often. Even though your drive becomes unreadable suddenly, you won't be too hurry-scurry.
  6. Install anti-virus software and scan your disks routinely


This post walks you through the process of repairing the unreadable disk and teaches you how to initialize the disk to get rip of "The disk you inserted was not readable by this computer" error. Hopefully, you have fixed your unreadable USB disks, flash disks, HDD, SD cards, or other disks.

What's more, iBoysoft Data Recovery for Mac is a powerful data recovery tool that you can rely on if you failed to fix the error by yourself.