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Can't format corrupted USB on Mac? Unable to write to the last block

Hello. My USB drive, which is formatted in Mac OS Extended (Journaled), got corrupted when I was copying files to it. The drive's partition map is Master Boot Record and has only one partition. When I connect it to my Mac, it won't mount. I tried to format it but failed because it somehow set it self to read only and says it was unable to write to the last block of the device. I also tried running First Aid on the drive but it did nothing.

Best Answered by

iBoysoft author Jenny Zeng

Jenny Zeng

Answered on Monday, April 29, 2024

The error "Unable to write to the last block of the device" usually indicates that the external hard drive has bad sectors or is failing. But it could also be caused by software issues. Give the following solutions a try. If they don't work, you may need to replace the drive.

Be reminded that erasing a drive will remove all data on it. If you have important files on the drive, you need to restore them beforehand. In your case, you'll need data recovery software to access your data. Remember to choose one that's capable of retrieving lost data from corrupted and inaccessible USB flash drives and is compatible with your macOS version and processors.

From my own experience, iBoysoft Data Recovery for Mac is a fair choice. You can use it to preview the lost files before recovery for free.

After your data is secured, try to:

  • Run First Aid on both the partition and physical disk to see if any issue is detected.
  • Use a different USB cable, port, or disk enclosure.
  • Connect your drive directly to Mac.
  • Securely erase the drive by clicking "Security Options" and moving the slider to the second option.
  • Format the drive on a different computer.
  • Execute the command diskutil eraseDisk file_system disk_name /dev/disk_number to erase your disk in Terminal.
  • Erase the drive after restoring it from a blank image created in Disk Utility.

For more details about these solutions, keep reading the following posts: 

How to Fix 'Unable to write to the last block of the device' 69760?

[Fixed] Disk Utility Won't Let You Erase Hard Drives


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