I got this pretty cool flash drive as a gift and I can't seem to use it. Every time I plug it in, a pop up comes up that says: The disk you inserted was not readable by this computer.

I opened up Disk Utility and tried to erase it, in the hope of making it readable. It shows the loading bar and after a couple minutes, a pop-up appears and says: Disk Erase failed with the error: Unable to write to the last block of the device. So I remove it, and try again with no avail. I even tried using terminal and the diskutil eraseVolume command and I get:

newfs_hfs: write (sector 0): Invalid argument

Mounting disk

Could not mount disk2 with name (null) after erase

Error: -69832: File system formatter failed

So I tookit out, and tried again with diskutil randomDisk just to see if I couldeven write on it. and then I got this:

Started erase on disk2
Error: -69879: Couldn't open disk
Underlying error: 2: POSIX reports: No such file or directory

Does anyone have any idea how I can make this drive readable?

  • Do you have turned on encryption on that drive? Do you have setup CoreStorage for that disk? – bot47 Feb 14 '12 at 11:58
  • That would be useful if you had provided make and model for the drive you could find in System Profiler under USB tab – iskra Feb 14 '12 at 23:40
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    Is your goal to erase the drive or to make it usable? "Can anyone help" isn't the best question without specifying what you want help with. Your title suggests that your issue is that you can't erase the drive, but if you were never able to write to it in the first place, erasing is likely not your problem. – Daniel Feb 15 '12 at 2:58
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    It shouldn't be this hard. My bet is that the drive is faulty. – jaberg Feb 15 '12 at 22:17
  • @Daniel I want it to be usable. – 0x60 Feb 16 '12 at 0:56

You've said in your question that you've been trying to erase the flash drive; not format it. Try formatting instead by doing the following:

  • Open Disk Utility
  • Select your flash drive
  • Select the Partition tab
  • Select Partition 1 under Partition Layout
  • Name the drive what you want under Partition Information
  • Make sure Mac OS Extended (Journaled) is selected under Format
  • Select Apply
  • Now sit back and watch your Mac do the rest
  • Rejoice!

Let me know if this works, or if you have any other questions. Good luck!

  • I get the error Partition failed with the error: Unable to write to the last block of the device. – 0x60 Feb 14 '12 at 0:42
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    The device is probably busted then. Hope you kept the gift receipt! – user14395 Feb 14 '12 at 15:30

Can you get the disk identifier? In Disk Utility, select the drive and choose "Info" – it should read something like disk1 or disk2 or so. (But NOT disk0; that's your internal HD!)

Then open a terminal, and type in

sudo dd if=/dev/zero of=/dev/diskX

(where diskX is of course the disk identifier you got earlier.)

Type in your admin password, and it should overwrite every block of the disk with 0x00 (i.e. erase it).

Then, you can format your drive.

[Please be cautious when doing this; I'm not responsible for anything if anything goes wrong ;-)]

  • How long should this take? – 0x60 Feb 10 '12 at 3:03
  • Not super long. I don't have exact numbers, but it should take an hour or less for average USB drives. – jan.h Feb 10 '12 at 16:52
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    Left it on for over 14 hrs. and it's still running. I looked in Activity Monitor and the process isn't hanged. – 0x60 Feb 10 '12 at 23:15
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    Sounds as if the usb drive is broken. – bot47 Feb 13 '12 at 9:57
  • I bet it is... But I hope not. – 0x60 Feb 14 '12 at 0:40

I had this problem with an USB stick in our Xbox 360. It would gave errors and could not be formatted on my iMac. I configured the stick first in the Xbox and after that there was no problem in partitioning it on the Mac.

It appears that the USB device was still in some kind of "busy-mode".


I was encountering the same error and discovered it was an issue with my mac mistakenly thinking the SD card was locked. Apparently the sensor in macbook pros and air can get stuck.

Crazy, but after hours trying different things in terminal and disk util, the solution was to blow really hard in to the SD drive then remount SD card and erase it as per instruction.


need to reinstall the firmware of the drive using a windows computer


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