Why the Disk You Inserted Was Not Readable by This Computer?
Usually, this error alert means that the directory of the drive has been corrupted.
The following solutions are worth trying.

Then, go to the next step to have a try.
In this situation, you could press theIgnoreoption and then search for a corresponding software to remove the encryption.
Thus, you might use another USB cable and USB port to check whether this issue disappears.
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If not, go to the next fix.
USB port not working?
Here is what you should do:
However, in some cases, the First Aid process fails finally.
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And you will receive a message like this:First Aid has failed.
If possible back up the data on this volume.
But, you should probably know that erasing a drive will delete all data on it.
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Thus, youd better rescue its files before erasing it.
you might directly erase the drive.
However, erasing the drive will delete all data on the drive.

If there are important files on it, youd better rescue them first and then erase the drive.
Perhaps, you are looking for afree Mac data recovery tool.
Stellar Data Recovery for Mac is worth trying.

from MacBook Pro/Air, iMac, Mac mini, and more.
The supported devices are also various including SSD, HDD, SD card, USB, etc.
Now, you might go to theMiniTool download centerto get this software.

Open Stellar Data Recovery for Mac.
Here, we takeRecover Everythingas an example.
After turning the switch of Recover Everything toOn, clickNextto continue.
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On this interface, you gotta opt for drive that you want to recover.
Then, clickScanto continue.
The software will begin to scan the selected drive.
you better wait until the whole process ends.
When the scanning process ends, you will see the scan results.
There are three list categories.
If you are a personal user, the Premium Edition can fully meet your requirements.
After all, some serious situations can prevent you from recovering data.
Here are three things you’ve got the option to do:
1.
Is it necessary to eject a USB drive properly from Mac?
The short answer is probably not.
But, there are still some risks which are mentioned in this post.
The well-known backup tool on Mac OS is the snap-in Time Machine.
They have been proved to be effective.
Hope they can help you out.
it’s possible for you to also share your ideas and suggestions here.