A while back, I tried installing OS X Snow Leopard on a USB Thumb Drive (64GB) in order to see whether it could run on a Mac with a broken HD. It worked, but was obviously incredibly slow (I didn't have an external hard drive to test with at the time).

Now I have the Mac fixed, but I'm having problems with the USB. It still has MacOS on it, but I want to erase it.

Here's what I tried on macOS High Sierra: Disk Utility -> Select the drive (grayed out) -> Erase: Gives error "Cannot write to last block of device"

On Windows: Command Prompt:

list disk
select disk 1
Error: Request could not be completed because of an I/O error.

On Ubuntu: GParted -> Select my disk -> Delete MacOS X partition

Gives error: Error fsyncing/closing /dev/sdb: Input/output error

This might not be the right forum to ask about this, but I figured it was caused by OS X, so I put it on here. I anyone has a suggestion of a better forum to go to, please tell me.

Does anyone have any idea how I might fix the USB Drive?


"Cannot write to last block of device" is usually a connectivity error - it often crops up on HDs & SSDs with a bad cable.

For it to happen on a USB stick, then I'd say either the contacts are dirty or the device is dead [or dying].

You could try cleaning up the contacts with a bit of contact cleaner, then push/pulling the stick a dozen times in & out of a [non-powered] USB socket.

If that gains nothing, then I'm reasonably certain that if it's failing on three different machines, then it's had it.

  • Ok. It was a brand new USB, so I don't understand why it would be broken already, buy I'll try it. – Caleb H. Feb 4 '19 at 13:23

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