Cannot format USB drive

Discussion in 'macOS' started by iTarbuck, Apr 22, 2019.

  1. iTarbuck macrumors member


    Jan 29, 2019
    Liverpool, UK.
    I have been trying to figure this out for a while now!

    I have a 32gb Kingston DTSE9 USB 2.0 flash drive, that my mac cannot view or read at all. It does not show on the desktop or in finder, and partitions are not shown in disk Utility. I can run first aid, which works fine but then erasing, restoring or partitioning fails every time.

    I am pretty savvy (software developer) but cannot get to the bottom of this. I have lots of other flash drives hanging around, so do not need this to be fixed but I do hate wasting hardware.

    Any ideas?
  2. chown33 macrumors 604

    Aug 9, 2009
    My first guess is that the hardware itself has failed. I've certainly had USB thumb drive failures that were hardware, and I simply trashed the device by drilling holes through it before discarding it. I've also had flaky USB connectors, where a little careful bending of the housing corrects it long enough to get data off.

    If you can get the device to attach (/dev/diskN), but the partitions won't mount (diskNsM), then you might be able to use 'dd' and/or 'diskutil' to play around with it.

    If you want to read the partition map, you can 'dd' it to a file, then compare to a known-good partition map and see what differs.

    Another thing to try with 'dd' is writing a couple hundred MB from /dev/zero to the /dev/diskN device, effectively overwriting the partition map with zeros. You'll probably need to be root, so 'sudo' is your friend.

    It's only 32GB and USB 2.0, so I'm not sure how much time it's worth, unless you're in it for the learning experience.

    Also see: 'cmp', 'diff', 'hexdump', etc.
  3. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    Building on what the previous poster said, try writing to the flash drive with dd. If can do a read but not a write, then it maybe in read-only mode. The flash drive needs to be un-mounted to do this but it sounds like it doesn't mount anyway. I have a flash drive that was encrypted - I'm asked for the password, I enter it, nothing happens. So it appears that macOS needs to write or requires that a volume be writeable before mounting a encrypted HFS+ (Core Storage) volume. So the system can see the drive, but doesn't mount and doesn't deliver any error messages. I keep the drive because it's good example of this situation. I have dd read from the drive and written it to another drive and the other drive works fine - the data appears to be OK (it was lossy compressed data and the resulting file seems fine but I'll never know if it's 100% because it is lossy and I don't have or don't care to look for the exact settings I used and the files seem fine compared to the files they were compressed from).
  4. Fishrrman macrumors P6


    Feb 20, 2009
    "I have a 32gb Kingston DTSE9 USB 2.0 flash drive, that my mac cannot view or read at all."

    Do you have A DIFFERENT MAC, or a PC that you could plug the drive into?
    Try doing so, and see if you can erase the drive there.

    If that works, bring it back and try it on the Mac (that won't format it) again.

    Or... if you're able to cleanly re-format it using another computer, just "use it" as it is.

    Sometimes flash drives just "go bad" on you... POOF!
  5. dwig macrumors 6502a

    Jan 4, 2015
    Key West FL
    I've encountered several drives that would fail to mount on macOS and on Windows. Usually the drive will be accessable from Windows' Drive Manager even when the logical volume won't mount. In such cases using Drive Manger to delete the partition, create a new partition, and then formatting brought the thumb drive "back to life".

    I've also used the SD Card Formatter that is distributed by the SD Association at: This is intended for use with SD cards of various flavors but I've had it work on problem USB thumbdrives. Even if it doesn't help this time, it is a small and free tool to keep at hand.
  6. uniquexoxo macrumors member


    Aug 27, 2018
    South East Asia
    Maybe you need to install an NFTS for Mac. This is the same case as my 1TB Passport Hard drive.
  7. cococheaf macrumors demi-god


    Jul 10, 2018
    Austria - Lake of Constance
    i would try the hardcore method: first, get the device id of the usb device via terminal: diskutil list -> note the /dev/*** name of the usb device. then enter "sudo dd if=/dev/random of=/dev/*** bs=4M".
    after that you should have a bit-mixed device, which should not contain any more old data/partitions/etc.
    then you can open disk utility and partition (not format) the drive.

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6 April 22, 2019