How to Fix the "Flash Drive Not Readable on Mac" Error

When you connect an external drive to your Mac but receive the error message "The disk you attached was not readable by this computer," what’s going on? Flash drives not readable on Mac is not something rare, which means you can find a lot of useful solutions to solve the issue.

Do Some Basic Checks

Before moving to some advanced ones, we suggest you first check the following peripherals to do a basic rule-out:

All of them are working just fine? We'll dig for more possible reasons why the disc you attached was not readable by this computer, and explain solutions accordingly.

Why Is My Flash Drive Not Being Read on My Mac?

When your Mac says, "The disc you attached was not readable by this computer", it means that the system is unable to read the data from the attached flash drive. Since you have excluded connection errors, the unreadable flash drive on Mac typically arises when:

• The flash drive is encrypted.
• The file system of your flash drive is corrupted or damaged.
• The flash drive is infected with a virus attack.
• You eject the flash drive improperly without safely removing it from macOS, causing data corruption.
• The external drive is new or hasn't been initialized/formatted to a compatible file system with macOS.
• You have just been through a macOS update - a typical macOS fault can make flash drives unreadable.

Knowing the causes, we can tackle each one with solid solutions as follows.

6 Solutions to Fix Flash Drive Not Readable on Mac

Is the flash drive showing up in both Disk Utility and Finder? If the external drive appears in Disk Utility but does not show up in Finder, it could be a mounting issue, or the disk is not initialized. Regarding the former situation, a simple Finder relaunch might do the trick.

However, when the disk is uninitialized, corrupted, or not mounting due to file system issues, you will need the following solutions for real problem-solving.

Check the File System Compatibility

One of the most common reasons for the "flash drive not readable on Mac" error is that your flash drive is formatted with a file system that macOS doesn't work well with, such as NTFS. For users who initialized the flash drive on Windows, you are likely to have an NTFS-formatted external drive.

To find out which file system your external drive runs, open Disk Utility on your Mac (Applications > Utilities). Select your flash drive and look at the file system format.

If it's NTFS, you can erase the drive and reformat it to exFAT or FAT32, both of which are supported by Mac and Windows. Unfortunately, reformatting your flash drive will wipe away all the data on the drive, so make sure to back up important files before proceeding.

Repair the Flash Drive

Another chance is that the flash drive is compatible but still not working, in this case, it could be due to a corrupted file system. Luckily, macOS offers a built-in feature in Disk Utility to help you repair the drive. Here’s what to do:

1. Open Disk Utility from Finder > Applications > Utilities.
2. Select the unreadable flash drive from the sidebar and click First Aid.

   

3. Click Run to allow macOS to check and fix any file system errors on the drive.

However, if First Aid reports that the drive is beyond repair, you may need to consider reformatting the drive.

Initialize the Flash Drive

If your external hard drive or flash drive is not initialized, macOS recognizes the drive but is unable to access its volume properly. As a result, you might see a message in Disk Utility stating that the disk is not initialized. Here’s how to fix it:

Step 1: Search for the external flash drive in Disk Utility. If the disk appears but is labeled ‘Untitled’ or ‘Unknown’, proceed with the steps below.

Step 2: Locate the uninitialized disk and click Erase. This will format the disk so macOS can recognize it.

Step 3: You’ll be asked to select a scheme for the drive. For cross-platform use between Mac and Windows, exFAT is recommended. Then give your drive a recognizable name.

Step 4: Click Erase again to confirm the action.

Ensure the Disk Is Not Encrypted

When your flash drive is encrypted, macOS will not allow you to access its contents without the correct decryption password. To find out whether it’s an encrypted disk or not, look at the drive’s information displayed in Disk Utility.

If the drive is encrypted, it will indicate an encryption status, such as FileVault Encrypted or APFS (Encrypted). You can enter the correct password to gain read-write access to the drive.

Upgrade or Downgrade Your macOS

Flash drive not readable on Mac has somehow become a classic macOS upgrade fault, particularly occurring in WD and LaCie drives. If you just upgraded your MacBook to a new version, you can either wait for the next update package to fix minor bugs or consider downgrading your macOS for urgent flash drive use.

Use Antivirus Software

Have you saved any suspicious files to your drive not long before it became unreadable? If so, it’s highly likely that the flash drive is virus-infected. To confirm that, rescan the flash drive in Safe Mode, which can also prevent virus processes from interfering. Once you have identified the virus, use trusted antivirus software to get rid of the malware for good.

Conclusion

After reading the post, hopefully, you know how to deal with the "flash drive not readable on Mac" error or "the disc you attached was not readable by this computer" prompt. These flash drive errors on Mac can be troubleshot by six main fixes, including checking hardware connections, repairing corrupted file systems, reformatting the drive to a macOS-compatible format, etc. For encrypted or virus-infected drives, decryption tools or antivirus software often restore accessibility