[Solved] How to fix 'The disk you inserted was not readable by this computer' on macOS?

Updated by Admin to Mac Data Recovery on June 9th, 2019

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

After plugging an external drive (A USB drive, flash drive, SD card or external hard drive) to your Mac, you can't get access to the external drive, as you get error message saying "The disk you inserted was not readable by this computer with three buttons: Initialize, Ignore, or Eject?" and cannot access the important data stored on it.

The disk you inserted was not readable by this computer

If you are using the previous Mac OS X operating system, the above error message is: "The disk is unreadable by this computer, do you want to initialize the disk?"

The disk is unreadable by this computer

"The disk you inserted was not readable by this computer" message usually means that the directory of the drive has become corrupted. Corruption can happen for a number of reasons:
Virus Infection
Catalog file corruption
Internal file system errors
Disconnecting or power off the drive without unmounting it
Forcing a restart on the computer
Experiencing a software lockup while writing to the drive
Turning the computer off without doing a proper shut down

Following are 4 steps to fix 'The disk you inserted was not readable by this computer' error.

Step 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 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, this new drive can be used to store the data.

3) Check it on another computer

Plug this disk into another Mac computer. If this error continues, please go to step 2.

4) 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.

Step 2: Repair unreadable disk with Disk Utility

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:

1) Please 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.

2) Select the unreadable disk from the left panel in Disk Utility.

3) Click First Aid button at the top of Disk Utility window.

First Aid built-in Disk Utility

4) Click Run button and First Aid will check the volume for errors and then repair unreadable disk if necessary. If First Aid fails to repair unreadable disk, please go to step 3 to recover data from unreadable disk.

Step 3: 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 data from unreadable hard drive, recover deleted files emptied from Trash, recover data from formatted drive, recover data from deleted/lost APFS partition, recover data from APFS drive, etc. on macOS 10.14 Mojave/10.13 High Sierra/10.12 and Mac OS X 10.11/10.10/10.9/10.8/10.7.

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

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 lost important data.

Step 4: 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 Mojave 10.14/High Sierra 10.13/Sierra 10.12 and Mac OS X 10.11/10.10/10.9/10.8/10.7 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.

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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