If your USB drive is corrupted on Mac, don't format it immediately—especially if it contains important files. First check whether the drive appears in Disk Utility. If it does, run First Aid to repair file-system errors. If First Aid fails, recover your important files before reformatting the USB drive.
If the drive doesn't appear in Disk Utility at all, check the USB connection, port, adapter, and the drive itself because the problem may be hardware-related rather than file-system corruption.
Quick Decision Table
| Situation | Likely Cause(s) | What to Do First |
| USB appears in Finder but files won't open | File system corruption | Run First Aid Or run Terminal |
| USB appears in Disk Utility but isn't mounted | File system likely broken | Go to data recovery |
| USB appears in Disk Utility but First Aid fails | File system corruption Severe file system damage Bad sectors Partition table corruption Drive hardware failure | Recover data first and reformat the USB drive |
| USB doesn't appear in Disk Utility at all | Possible connection or hardware issue | Check port, connection, power, and another Mac Turn to a professional repair service |
Before Repairing a Corrupted USB Drive
Before you proceed to repairing a corrupted USB drive on Mac, you'd better do as follows:
- Back up accessible files
- Don't rush to format your USB drive
- Don't save the recovered files back to your damaged USB drive
- Stop software repair and turn to the professional repair service if physical damage is suspected
How I Tested the USB Repair Methods
I tested the repair workflow on a 13-inch MacBook Air 2017 running macOS Monterey 12.7.6 with a 62.02GB Kingston DataTraveler 3.0 Media USB flash drive formatted as an NTFS file system. I first verified that the drive appeared in Disk Utility, then ran First Aid and recorded the result. For the failed-repair scenario, I recovered the accessible files before erasing and reformatting the drive.
Run First Aid in Disk Utility to Fix 'USB Mounted But Unreadable' Issue
If your USB drive is successfully mounted in Disk Utility but is unreadable, use Mac First Aid to repair disk.
Here I shared my actual test with First Aid to repair an unreadable USB on Mac:
Step 1. Connect my Kingston DataTraveler 3.0 Media USB drive to my MacBook Air (2017) via the USB port.
Step 2. Click Launchpad > Type "Disk Utility" > Open it.
Step 3. Click View > Show All Devices.
Step 4. Choose my USB drive "Kingston DataTraveler 3.0 Media" > click "First Aid" in the top menu > tap Run.
If your USB drive contains a container, run First Aid on the container as well. My Kingston USB drive has only two volumes: one is a BitLocker-encrypted exFAT volume, and the other is NTFS. Therefore, I need to select the entire USB drive and run First Aid on it.
Step 5. First Aid runs very quickly on my Kingston USB drive, taking less than 10 seconds to complete. It successfully repairs the unreadable USB drive, and Disk Utility displays an "Operation successful" message.
What to Do If First Aid Failed to Repair the USB Drive?
If First Aid failed to repair your disk or your USB drive appears in Disk Utility but is unable to be mounted, recover your data first and reformat the USB drive second!
To recover data from a USB on a Mac, you can try a dedicated data recovery utility.
Recover Data from an Inaccessible USB with iBoysoft Data Recovery for Mac
iBoysoft Data Recovery for Mac is able to recover documents, pictures, audio files, videos, Emails and other types of files from a corrupted, inaccessible, unmountable or formatted USB drive. Meanwhile, it can also restore files from lost disk partitions, including deleted or missing APFS or HFS+ partitions.
It works well with both Intel and Apple Silicon Macs, from OS X El Capitan 10.11 to macOS Tahoe 26.
Note: Stop using the affected drive before data recovery. Do not repair, erase, format, or save new files to the disk before iBoysoft Data Recovery for Mac scans it. Meanwhile, make sure your USB drive can be detected by Disk Utility.
Step 1. I Downloaded and installed iBoysoft Data Recovery for Mac version 5.2.4 on my MacBook Air. Allow the extension.
Step 2. I connected my external Kingston DataTraveler 3.0 Media USB drive to my Mac, and then launched iBoysoft Data Recovery for Mac.
Step 3. Select the inaccessible USB disk or a logical volume. Here I chose the whole external disk for scanning and click "Search for Lost Data" to scan for all lost files.
Since I chose to scan the entire external disk, the scan takes longer—about 40 minutes. The scanning time largely depends on the amount of data on the disk and the scanning mode the software auto-selected (Quick or Deep).
If your important data is stored on only one volume, you can select that specific volume to scan and recover instead. This can significantly reduce the scanning time.
Step 4. Preview the scanning results to make sure these files are in good condition.
Step 5. Choose files you want to get back and click "Recover".
Step 6. Save the recovered files to another healthy and accessible disk and then check to ensure all lost files have been successfully recovered.
Reformat the Corrupted USB Drive
After you get your files back from the USB drive, then you can feel free to reformat it to fix the original file system corruption. Please see the steps below to reformat a problematic drive.
• Guide to format USB flash drive on Mac
This will assign a new file system to this corrupted USB drive so that it can be usable again. However, if reformatting can't repair your disk then we recommend responsibly recycling it as long as you've successfully recovered your files as we explained earlier.
What If the USB Doesn't Appear in the Disk Utility?
When the USB drive doesn't even show up in the Disk Utility, this might result from USB port problem, cable/adapter problem, insufficient power, device-controller failure, or physical damage.
In this scenario, check port, cables, and power, and the device may require professional service.
When Should You Stop Trying to Repair the USB?
If the USB drive is physically cracked, bent, water-damaged, unusually hot, repeatedly disconnecting, or not detected by any computer, stop using it if the data is important. Software repair tools cannot fix failed flash memory or a damaged controller. Consider professional data recovery instead.
How to Prevent External USB Drives from Corruption?
Storage media like USB flash drives, SD cards, etc. are prone to corruption because they are frequently attached and removed for transferring files between different computers. While a regular backup is the best way to avoid data loss when a drive won't work normally, here are a few tips to prevent disk corruption that will help prevent data loss:
- Eject the USB before unplugging it
- Don't disconnect during file transfers
- Avoid physical damage, heat, and moisture
- Keep important files backed up
- Replace a USB drive that repeatedly develops errors.
FAQs
- Q1. Can I repair a corrupted USB drive on Mac without losing data?
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A
Sometimes. If the USB drive is still accessible, back up your important files before attempting any repair. You can then use Disk Utility's First Aid to check and repair certain file-system errors. If First Aid fails and the files are important, recover the data before reformatting the USB drive, because formatting erases its existing data.
- Q2. How do I know if my USB drive is corrupted on Mac?
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A
Common signs include files that won't open, folders that appear empty or inaccessible, repeated read/write errors, the USB drive not mounting, or Disk Utility reporting file-system errors. However, if the USB drive doesn't appear in Disk Utility at all, the problem may be a connection or hardware failure rather than simple file-system corruption.
- Q3. What should I do if First Aid fails to repair my USB drive?
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A
If the USB contains important files, don't immediately erase or reformat it. First try to recover or back up the important data. After the data is safe, you can erase and reformat the USB drive. If the drive is physically damaged, repeatedly disconnects, becomes unusually hot, or isn't detected by multiple computers, stop using it and consider professional data recovery.
- Q4. Does formatting a corrupted USB drive fix it on Mac?
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A
Formatting can fix many logical file-system problems by creating a new file system, but it does not repair physical hardware damage. It also erases the existing data on the USB drive. Therefore, recover or back up important files before formatting a corrupted USB drive.