Fix "The disk you inserted is not readable by this computer"

Updated by Tim to Mac Data Recovery Tips on March 11th, 2020

Summary: This post will show you 7 solutions to fix disk unreadable error on the storage device.

Some users are experiencing "The disk you inserted was not readable by this computer" error when connecting an external drive to their Mac computers.

The disk you inserted was not readable by this computer

Some affected users report the issue occurs with every external drive. While others say this unreadable disk error only appears with one external drive.

Most of the time, this issue happens on macOS, but it also occurs on Mac OS X. The error on Mac OS X is "The disk is unreadable by this computer, do you want to initialize the disk?".

The disk is unreadable by this computer

Why does Mac say "The disk you inserted was not readable by this computer"?

Virus infection
Hardware issue
The disk is not formatted
Catalog file corruption
Disk structure is corrupted
File system is corrupted
Forcing a restart on the computer
The file system of the disk is not supported by macOS
Disconnecting or power off the drive without unmounting it
Experiencing a software lockup while writing to the drive
Turning the computer off without doing a proper shutdown
Disk failure - It is possible that either the disk itself or just its USB interface has failed. In this case, a data recovery solution is advisable.

Solution 1: Determine if the disk has a problem

1. Check if the disk is encrypted

If you receive disk unreadable error after inserting an encrypted drive, you need to open this drive with the corresponding app.

If the disk is encrypted by Bitlocker, try M3 Bitlocker Loader for Mac to access Bitlocker encrypted drive on Mac.

If the unreadable disk is encrypted APFS file system, try M3 Data Recovery for Mac to recover lost data.

2. Check if the file system is not supported by macOS

Check the file system of the external drive to see if the file system is supported by macOS. If macOS isn't compatible with this file system, the disk you inserted is not readable by this Mac. For example, ReFS file system is not supported by macOS.

3. Check if the disk is a new hard drive

If it is a new hard drive, click "Initialize" button to initialize it after seeing unreadable disk error. After initializing it, this new drive will be working.

4. Check the disk on another computer

Plug this unreadable disk into another Mac and check if it can be readable. If this error continues, please try other solutions as below.

5. Change USB cable and USB port

Sometimes, USB cable or USB port is something wrong so that the disk is not readable by this computer. In this case, please change another USB cable or USB port and try again.

6. Reset USB port

If you're confident USB port is a problem and not the device, the first thing you should do is reset SMC. It is a simple process which is slightly different depending on the Mac hardware.

Solution 2: Re-insert the drive

You can try simply re-connecting the hard drive to your Mac. Just safely remove it from your Mac and then re-plug it. Then, attempt to access it and see if the error persists. If this error still occurs, please move on and try following solutions.

Solution 3: Update the drivers on your Mac

The disk unreadable error can also be caused due to an outdated driver on your Mac. You can check the drivers on your Mac and update them via the following steps:

Step 1: Go to Apple menu and select "System Preferences..".

Step 2: Click "Software Update".

Step 3: Check for any available updates for your system and applications.

Solution 4: Fix disk unreadable error with Disk Utility

This error should be repaired using Disk Utility. It isn't guaranteed to work, but some users encountering the same error message have reported that the issue was resolved.

First Aid is a utility built-in Mac operating system. It can check and repair file system errors on Macintosh HD, external hard drive, USB drive, flash drive, SD memory card, etc,.

Steps to fix 'The disk you inserted was not readable by this computer' error with First Aid:

Step 1: When the initial prompt appears, click Ignore to dismiss it.

The disk you inserted was not readable by this computer

Step 2: Once the error has been dismissed, open Applications -> Utilities -> Disk Utility.

If Macintosh HD is not readable, please run First Aid from recovery mode. Restart your Mac and press & hold down Command + R keys at startup, then select Disk Utility from macOS Utilities panel.

Step 3: In the left panel of Disk Utility, select the problematic disk.

Step 4: Click "First Aid" button in the toolbar of Disk Utility.

First Aid built-in Disk Utility

Step 5: Click "Run" button, First Aid will check the volume for errors and then fix the problem if possible.

Wait until the procedure is complete. If you get returned a message saying success, restart your Mac and see if the disk becomes readable.

If another message says that disk utility cannot repair unreadable disk, go to solution 5 to recover lost data.

Solution 5: Recover lost data from unreadable disk

Due to the above causes, macOS fails to read the disk and you cannot access the data stored in it. To access the data, you can restore your data from the backup if you have a backup elsewhere. If you do not have a backup, you need a professional Mac data recovery software to recover lost data.

As a professional Mac data recovery software, M3 Data Recovery for Mac can recover deleted files emptied from Trash, even recover lost files from unreadable drive, formatted drive, recover lost data from deleted/lost APFS partition, etc.

M3 Data Recovery for Mac is fully compatible with macOS Catalina 10.15/Mojave 10.14/High Sierra 10.13/10.12 and Mac OS X 10.11/10.10/10.9/10.8.

Tutorial to recover lost data from the unreadable disk on Mac

1) Download, install and launch M3 Data Recovery for Mac software on your Mac.

2) Select the unreadable disk.

Mac data recovery software

If the unreadable disk is encrypted APFS, click "Find Lost APFS Partitions" at the top to recover lost data. Because encrypted APFS drive data recovery requires the password to decrypt the data.

3) M3 Data Recovery for Mac software is scanning the data from the unreadable disk.

Scan lost data from unreadable disk

4) After the scan completes, you can preview the documents, photos and play videos, audios. Click Preview button and check if your lost files are recoverable.

Recover lost data from unreadable disk

Tips: If the above solution fails, please choose the volume and scan again.

5) Select the files you need and click Recover to start recovery.

If the disk is still not readable by M3 Data Recovery for Mac, send it to a local data recovery professional.

Solution 6: Initialize the unreadable disk

After data recovery is successfully done, erase this disk to repair disk unreadable error with the following steps:

1) Launch Disk Utility from Utilities in Applications folder.

2) Select this unreadable disk at the left sidebar of Disk Utility.

3) Click "Erase" button in the toolbar of Disk Utility.

Erase the drive

4) Select file system and then click "Erase" button, the unreadable disk will be working again after erasing.

Solution 7: Ask a professional for Help

Nevertheless, some users may worry that their own improper operations will make further damage to their hard drives. In this scenario, you'd better take it to the professional. They could give you some correct suggestions to help get rid of this error.

How to avoid disk not readable error again

1. Eject external drive properly

External drive is easy to be corrupted if you eject the external drive improperly. If you remove external drive from the computer when being in use, it can also be corrupted. So you must safely remove external drive from the computer by clicking "Safely Remove Hardware" option.

2. Back up important data

Data backup is the best way to prevent data loss. Time Machine is a macOS built-in data backup software which can automatically back up all of your files.

3. Use advanced file system

If you have a choice, please adopt NTFS (APFS, HFS+) file system instead of FAT32/exFAT file system. NTFS file system gives you more flexibility in length of filenames and directory, security control. What's more, you can stand a greater chance of recovery in case of drive corruption.

Related articles: