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I have a 64 GB micro, formatted as exFAT, that I had been using in my Android phone and want to repurpose it for Windows with a USB 3.0 card reader. I've tried working with it in a Transcend USB 3.0 card reader and another USB 3.0 card reader without success.

Windows keeps complaining the volume bitmap is corrupt, the drive is "dirty", and won't let me do anything with it other than read files. Chkdsk with /F says "Corruption was found while examining the volume bitmap", which I'm assuming is in that first 16 MBs at the beginning of the card, which I can't seem to delete. Every time the card is inserted into my PC, Windows tells me to scan it, but then I don't get any messages back unless I run chkdsk /F from a CMD window.

I put it back in my Android 6.0 phone and asked it to format the card. It says it did, but then when I look at the card after the format is done. everything is still there. I did not tell to format as internal storage since that will encrypt the card.

I've used the SDFormatter v5 from sdcard.org. It recognizes the card and capacity correctly and says it formated the card okay. But the card still shows folders and files from my phone, and the first 16 MB "unallocated" partition is still there.

I've tried using diskpart, deleting the 2nd partition so the whole card is unallocated, doing a "clean all" which did nothing but waste a couple hours. I have tried several other partition manager programs including Paragon HD MGR 15, to delete the 2nd partition where the bulk of the space is.

They all show me the 2nd large partition is deleted and I see a fully unallocated card. But when I eject and reinsert the card, it comes back with that 16 MB area at the very beginning still as "unallocated", then the 2nd larger partition and Windows wants to scan the card again.

Nothing I have tried will delete that 1st 16 MB area. It's a micro SD card so there's no lock switch and I'm not using it in a standard size adapter that has a write protect switch.

From what I've read, I think this is something to do with storing the info used to encrypt the card. I don't recall ever telling my phone to encrypt the card but I may have.

I just want to blow away everything on the card, whether or not it's encrypted, and have a clean, fresh card to reuse. At this point, Windows can read from the 7 or so gigabytes of files on the card, so I don't think it's actually encrypted, but refuses to write new files or let me erase files.

I'm surprised that SDFormatter utility from sdcard.org claims it worked fine but that 16 MB partition is still there and the card can only be read from and not written to in Windows. That is supposed be THE utility one should use to properly initialize and format SD cards.

At this point, I'm stumped, so I'd welcome any ideas for totally wiping the card so I can use it again.

TIA, Mark

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3 Answers 3

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I had a similar problem with a Samsung EVO Plus SDXC 128 GB card, where I was puzzled that my changes to the file system disappeared after the card was removed from the drive. It turned out that the card was broken and I couldn't write to it although no error was reported when I edited files and their contents appeared changed. However once I removed the card or rebooted my Raspberry Pi nothing had changed.

So maybe your card is broken. I got mine replaced by Samsung for free.

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  • Someone suggested breaking the card in half prior to returning it to Samsung to make it unreadable so any personal data can't be recovered from it by Samsun.
    – SDMark
    Commented Apr 12, 2020 at 0:17
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According to a quote attributed to SanDisk support, the 'empty' 16MB partition is intentional and permanent:

"You may leave the 16MB unallocated space as it is. A portion of the total capacity is used to store certain functions including optimizations of the memory that support performance and endurance and therefore is not available for user storage."

I found such a 16MB partition on my Samsung EVO Select 128GB card. I also read that 256GB cards may have a 32MB partition for the same purpose.

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    i disapprove the support answer greatly, they could easily hide the chip via firmware trimming the chip size. whats left seems marketing issues its a 128gib card (whithout paying for larger chips). yet 16mib.
    – droid192
    Commented Jan 31, 2020 at 20:18
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Windows supports only one partition on “removable” storage devices like USB thumb drives and memory cards. This is an artificial limitation.

To “wipe” the card: open diskpart. It will automatically run as admin.

  1. Use list disk to find your SD card. You need its number.
  2. Use select disk X to select the SD card.
  3. Make absolutely sure you selected the SD card.
  4. Execute clean.

You can now exit diskpart. Windows will ask you to format the device. Alternatively, you could run create partition primary and format fs=exfat quick to do so in diskpart.

If after all this it will isn’t working your SD card is probably somehow broken. Also make sure your card reader supports the relevant SD standard (SDXC).

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  • Thanks. I tried that. What I realized is that diskpart shows it as Partition 1, 59 GB, but, with a 16 MB offset. It "cleaned", and I've also selected parition 1 and deleted it. Still shows the same thing. It's the "offset" I can't seem to get rid of and I think that's what is messing up Windows 7.
    – SDMark
    Commented Jul 10, 2017 at 9:57
  • No, that offset is definitely not your problem. If after deleting the partition is still there, something is very wrong. Check with a different card.
    – Daniel B
    Commented Jul 10, 2017 at 10:29
  • Yes, it just comes back. Okay thanks, I'll look into it further.
    – SDMark
    Commented Jul 10, 2017 at 10:47
  • So far, nothing I've done has worked. I'll start a new question looking for a utility or program that can very, very low level overwrite any writable areas and just ignore any that can't be written to as I need to wipe the card before getting a replacement.
    – SDMark
    Commented Jul 27, 2017 at 2:13
  • If you’re concerned about data leaks, don’t return the defective card. There is no such thing as low level access. The SD card has a controller that manages accessing the flash memory.
    – Daniel B
    Commented Jul 27, 2017 at 6:36

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