Backup using File History files can't be deleted from USB drive  

My new 256 GB Sandisk Ultra 3.0 USB thumb drive originally showed up in Disk Manager with a main partition of around 248 GB and a system partition of around 200 MB.

I briefly used it in my Win10PC as a backup drive (Back up using File History).

I later went back in and designated a different (non-USB) drive as the target for “Back up using File History”.

But this did not remove 15 GB worth of old backup files from the thumb drive, and when I tried to erase them, permissions were denied. I looked and looked for a way to adjust permissions in order to get rid of them, without success, so I reformatted the thumb drive.

But now the thumb drive only has 233 GB free space. In Disk Manager it has a 200MB healthy EFI System Partition, and a 233GB NTFS Healthy (Basic Data Partition).

This suggests that around 15GB worth of backup files are still there, but now they are totally invisible and inaccessible.

Is there any way to get this thumb drive back to its original, larger capacity?

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(Windows 10 Pro ver 20H2 (OS build 19042.867)

Try this (note that this will remove all data from that thumb drive):

1) Open a command prompt.
2) Run the command "diskpart".
3) Wait uintil you see a "DISKPART>" prompt and then run the following command:

list disk

A list of all disks will be displayed. You should be able to tell from the size which disk the thumb drive is based upon the size. Note what disk number this is. In this example, I will assume "Disk 3".

Run the command "select disk 3" (use the disk number that you determined).

4) Run the following commands:

clean
create partition primary
format fs=ntfs quick
assign
exit

You should now be back at the command prompt again. Type in "exit" once more or simply close the command prompt window.

Did this help?

You can choose to overwrite the USB thumb drive thoroughly by diskpart. Run cmd as administraor and then type diskpart to open this tool. Then, type the following commands and hit Enter after each one.

• list disk
• select disk 1 (Note disk 1 is the number of disk you want to zero out.)
• clean all
• exit

After that, you can go to disk management and recreate partition for the USB drive.

Also, you can write zeros or use advanced disk wiping methods, such as, DoD52220.22-M, Gutmann, etc.