7 solutions to fix disk unreadable error on USB/SD card/external HDD/macOS Catalina/Mojave/High Sierra

Updated by Admin to Mac Data Recovery on January 10th, 2020

Summary: This article will show you how to fix 'The disk you inserted was not readable by this computer' on external hard drive, USB drive, SD card, flash drive, new hard drive, macOS Catalina/Mojave/High Sierra, etc.

Some users are receiving the "The disk you inserted was not readable by this computer" error at once when they plug an external drive (A USB drive, flash drive, SD card or external hard drive) into their Mac computers.

The disk you inserted was not readable by this computer

Some affected users report that the issue occurs with every external device that they connect while others say that the error only appears with one drive. Most of the time, the issue is reported to occur with MacOS, but there are reports of it occurring on Mac OS X versions with the error: "The disk is unreadable by this computer, do you want to initialize the disk?"

The disk is unreadable by this computer

What causes the disk not readable on Mac computer?

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.

The disk is unformatted - This particular error can also occur if the disk you've just inserted is not formatted or is formatted with a file system not supported by macOS.

Virus Infection

Catalog file corruption

Internal file system errors

Disconnecting or power off the drive without unmounting it

Forcing a restart on the computer

Hardware issue

Experiencing a software lockup while writing to the drive

Turning the computer off without doing a proper shut down

Solution 1: Determine if the disk has a problem

1. Check if the disk is encrypted

If you receive "The disk you inserted was not readable by this computer. There are three buttons: Initialize, Ignore, Eject" after inserting an encrypted drive, please choose "Ignore" and find the corresponding software to open it.

If the unreadable disk is encrypted by Bitlocker, please try M3 Bitlocker Loader for Mac to open/access Bitlocker encrypted drive on macOS.

If the unreadable disk is encrypted APFS file system, please try M3 Mac Data Recovery to recover data from encrypted APFS drive.

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 it is the file system that macOS isn't compatible with, it is the reason that the disk you inserted is not readable on 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, SSD, SD card, USB drive, flash drive, etc., please choose "Initialize" to initialize it after receiving "The disk you inserted was not readable by this computer" message. After initializing it, this new drive can be used to store the data.

4. Check it on another computer

Plug this disk into another Mac computer. If this error continues, please try other solutions as below.

5. Change USB cable and USB port

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

6. Reset USB port

If you're confident a USB port is the problem and not the device itself? The first thing you should do is reset the Mac SMC, a simple process which is slightly different depending on the Mac hardware, learn how to reset the SMC on all Macs here.

Solution 2: Re-insert the drive

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

Solution 3: Update Mac drivers

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

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

Step 2: Click on the "Software Update".

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

Solution 4: Repair unreadable disk with Disk Utility

If you see this error message as soon as you insert your USB drive, external hard drive, SD card into your Mac computer, you should be able to repair it using Disk Utility. This 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 the Macintosh operating system for checking and repairing file system errors on Macintosh HD, WD external hard drive, Seagate external hard drive, Toshiba external hard drive, WD My PassPort hard drive, USB drive, flash drive, SD card, memory card, etc,.

Please follow below steps to fix 'The disk you inserted was not readable by this computer' error with First Aid built-in Disk Utility:

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: Boot to Recovery mode by restarting the Mac machine and pressing & holding 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 disk that is showing the error.

Step 4: Click the First Aid button at the top of Disk Utility window.

First Aid built-in Disk Utility

Step 5: Click Run button and First Aid will check the volume for errors and then repair unreadable disk if necessary.

Wait until the procedure is complete. If you get returned a message saying that the procedure was successful, restart your Mac computer and see if the disk becomes available at the next startup.

If another message pops up saying that disk utility cannot repair unreadable disk, please go to solution 5 to recover data from unreadable disk.

Solution 5: Data recovery from unreadable disk

Due to the above causes, Mac Operating System fails to read the hard drive and the data stored in it becomes inaccessible. To access the hard drive again, maybe you want to run First Aid in Disk Utility. If you are experiencing the disk is unreadable error and you have a backup of your data elsewhere, use the Disk Utility to erase the drive and then restore your data from backup. If you do not have a backup, you need a professional Mac data recovery software to recover data from unreadable hard drive.

As a professional Mac data recovery software, M3 Mac Data Recovery can recover lost data from unreadable hard drive, recover deleted files emptied from Trash, recover lost data from formatted drive, recover lost data from deleted/lost APFS partition, recover lost data from encrypted APFS drive, etc. on macOS 10.15 Catalina/10.14 Mojave/10.13 High Sierra/10.12 and Mac OS X 10.11/10.10/10.9/10.8.

Tutorial to recover data from unreadable disk on Mac

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

2) Select unreadable disk.

Mac data recovery software

If unreadable disk is encrypted APFS file system, please click "Find Lost APFS Partitions" at the top right corner and then recover data from unreadable encrypted APFS drive, because encrypted APFS drive data recovery requires the password to decrypt data.

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

Scan lost data from unreadable disk

4) Select the found files you expect to recover and then click Recover to save them.

Recover data from unreadable disk

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

If disk is still not readable by any Mac data recovery software or has hardware issue, please send the unreadable disk to a local data recovery service for help if you need to recover important data.

Solution 6: Initialize the disk

After data recovery is successfully done, you can erase this unreadable hard drive, external hard drive, SD card, USB flash drive, memory card, CF card, etc. to fix 'The disk you inserted was not readable by this computer' error on macOS Catalina 10.15/Mojave 10.14/High Sierra 10.13/Sierra 10.12 and Mac OS X 10.11/10.10/10.9/10.8 with the following steps:

1) Launch Disk Utility from Utilities in Applications folder.

2) Click the icon for your hard drive in the sidebar on the left.

3) Click the Erase tab along the top of the window and enter the related information.

Erase the drive

4) Click the Erase button.

5) Select file system and then click the 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 you get rid of this error.

How to avoid disk not readable error again

1. Eject external drive properly

External drive (USB drive, flash drive, SD card, external hard drive, etc.) is easy to be corrupted if you eject external drive improperly. If you remove external drive from the computer when external drive is still in use, external drive can also be corrupted, so you must safely remove external drive by clicking "Safely Remove Hardware" option.

2. Back up important data

Data backup is the best way to prevent data loss. Time Machine built-in macOS is a data backup software which can automatically back up all of your files, including apps, music, photos, email, documents, and system files.

3. Use advanced file system

If you have a choice, please adopt NTFS (APFS, HFS+) file system instead of FAT32/exFAT file system. Not only it gives you more flexibility in length of filenames and directory, security control, but also you can stand a greater chance of good recovery in case of drive corruption.

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