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I had some problems with my USB stick so I wanted to erase it via Disk Utility but a "Operation failed" message appeared.

So, I am currently erasing it via Recovery Mode.

However, it is taking too long and it's stuck in "Mounting disk" message.

Any solution? What happens if I shut down my computer and just use another USB stick?

Please help ASAP.

Thanks.

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  • Which macOS are you using?
    – Bob
    Commented Feb 22, 2017 at 15:26
  • @Bob macOS Sierra. I unplugged it and plugged it in again and tried to erase it via Disk Utility but it says "couldn't open device".
    – NSD
    Commented Feb 22, 2017 at 15:28
  • Were those the exact words? I'm familiar with a dialog that says "The disk you inserted is not readable by this computer," but not "couldn't open device." Does it give an error code? (they usually look something like -1000)
    – Bob
    Commented Feb 22, 2017 at 15:35
  • Yes, check my recent question in my profile it contains a screenshot.
    – NSD
    Commented Feb 22, 2017 at 15:38

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Here's a trick that I've used before. On the Disk Utility sidebar, if you select the storage device, not the partition, you have the option to completely erase the disk and rebuild the partition table. It looks like this:

enter image description here

Compare this to what you see if you just try to erase and reformat the partition:

enter image description here Notice that the "Scheme" option is missing. If you use this option (which I believe is what you're trying to do), then it's trying to work with the existing partitioning and metadata, which has the potential to cause problems like what you're seeing.

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