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So I'm trying to erase the disk after making it to a bootable usb but now I’m getting this error "Couldn't open device". This happened before and after a reboot.

I've tried first aiding it first and erase it and using other format I've tried using terminal to erase, got the same error every time.

enter image description here

enter image description here diskutil list

/dev/disk0 (internal, physical):
    
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *121.3 GB   disk0
       1:                        EFI EFI                     209.7 MB   disk0s1
       2:                 Apple_APFS Container disk1         121.1 GB   disk0s2
    
    /dev/disk1 (synthesized):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      APFS Container Scheme -                      +121.1 GB   disk1
                                     Physical Store disk0s2
       1:                APFS Volume Macintosh HD            57.9 GB    disk1s1
       2:                APFS Volume Preboot                 44.7 MB    disk1s2
       3:                APFS Volume Recovery                512.4 MB   disk1s3
       4:                APFS Volume VM                      2.1 GB     disk1s4
    
    /dev/disk2 (external, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:                                                   *4.2 GB     disk2

So how can I erase /dev/disk2?

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3 Answers 3

Reset to default
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Have you selected a partition in Disk Utility, or the entire device?

Carbon Copy Cloner has an excellent, detailed set of instructions available online. You didn't tell us which macOS version you're using (in the future, remember that will help!), but this page has instructions from Catalina all the way back to Yosemite.

Let us know if you're still having problems after trying this.

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  • Yes, I've tried everything but still it says couldn't open device. I use macOS mojave
    – user13414903
    Commented Jun 4, 2020 at 8:28
  • I can't imagine what could be causing this... maybe a failed disk? Is it new, used - recently? Have you tried it in another system?
    – Seamus
    Commented Jun 4, 2020 at 8:35
  • It's new just bought it and im sure it's not broken
    – user13414903
    Commented Jun 5, 2020 at 6:41
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You can start disk utility and select the disk you want to erase. Now go to Partition in Disk Utility and adjust the size or add a partition. Doing this should erase your disk. if there are no partitions add one and make it include the whole disk!

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  • I forgot to write but i've tried erasing with disk utility but still couldn't open device
    – user13414903
    Commented Jun 4, 2020 at 8:27
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Since your USB key was not old, there are only 2 remaining causes to this USB key you cannot open through Disk Utility or through command line:

  • The USB female connector is dirty, to check this best case, just use a compressed air can to clean it. Next test again to open your USB.

  • Your USB was key damaged through an electric discharge. This could happen when an external device is disconnected when a write¹ operation is in progress. Due to the rapid voltage change on the connected USB key, an induced voltage peak will occur which could damage the internal electronic of the USB key. The damage will depend on how well the USB key was conceived to sustain such an electric over surge. This could also happen when you touch the conductive male USB connector when you have accumulated a lot of static electriciy ( for example upon removing a sweater made of synthetic fabric, the instantaneous electric voltage can reach 10000 V ). See also damage to electrical appliances by unplugging them. In this worst case, nothing will fix your USB. It is electronically dead. You will never be able to see the physical damage ( it requires breaking it and a microscope ), but just after the event you undoubtly smell it: specific smell of the produced ozone.

¹ Why write? Because inside moderne storage write requires more voltage to erase information.

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