How do you partition a USB Thumb / Flash Drive?

Out of the box, Windows will not allow you to partition a USB Thumb / Flash Drive. How can you do this?

In case anyone is wondering Why you would do this?

It's interesting in the case of a BitLocker ToGo drive where you can take a large thumbdrive (like 4 or 8 GB) and format a small amount of the drive to be used normally as a Fat32 drive and leave the remaining partition encrypted using BitLocker. This allows you to keep some non secret data on the unencrypted partition(like portable apps).

It can be done with a command line tool called diskpart

The steps (on Windows 10) are as follows:

1. Click the windows icon
2. Type cmd (do not hit enter)
3. Right click the 'Command Prompt' option (it was the first option for me), select 'Run as administrator' and click 'Yes' on the confirmation popup

4. Click into the 'Administrator: Command Prompt' window, type diskpart and hit enter (be careful from here on - you are doing low-level things to your drives and could delete your main drive if you're not careful)

5. You should see a DISKPART> prompt. Type list disk and hit enter. You'll get a list of drives back - you want to find the USB drive. It will probably be much smaller than your main drive. I'm using my system as an example - yours will probably be different so you're going to have to work out which drive is the USB drive. You don't want to get this wrong! If you are in any doubt, seek help from a more technical friend. You can destroy your data if you get it wrong!

For example, on my system I see:

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online         1863 GB    10 MB        *
  Disk 1    Online           58 GB      0 B        *

6. The USB drive in my case is Disk 1 (I have a 64Gb drive, 58 is close enough!). It's clearly not the 1863Gb Disk 0, that is my main Windows drive. I don't want to go anywhere near that one!

7. Now I want to select disk 1 and hit enter (It might be 2 or another number on your system. Almost certainly NOT 0.)

8. Now type list partition [enter] and you'll see the partitions on your USB drive.

9. I had a 200Mb EFI partition that I wanted to delete. It was partition 1 so I did select partition 1 [enter]

10. The EFI partition on my drive was protected, so when I tried to delete the partition, it failed. The command to force it is delete partition override. This will delete the selected partition. Note: I had to use the help system to figure this out: help delete partition [enter] gave me what I needed.

11. Once you've deleted the partition(s), you can go back into Disk Management and reformat / repartition the drive with the nice GUI :)

You can see all the diskpart commands by typing help [enter]. There's a lot there, but I prefer to do as little as possible in diskpart and then go back to the Disk Management GUI.

Out of the box, Windows Vista/7 allows the partition of an USB drive. The command is diskpart.

The problem

Contrary to Linux, Windows cannot partition or properly use a partitioned (USB Flash Drive) UFD; that is, if you plug a partitioned UFD, only the first partition will be visible.

The solution

The solution should address two problems: partitioning and make partitions visible. As for the first, an option is to use Linux, perhaps a live distro specifically targeted to imaging and partitioning, like Clonezilla. There are also free Windows tools like Bootice.

The second task is to make all (not only the first one) usable in Windows. A discouraged option is to use tools flipping the removable media bit, as they can damage incompatible sticks.

A better way is to install a filter. A program similar to a drive, adding extra functionality to them. In our case making an UFD appear as fixed drive. See for example Karyonix diskmod.sys discussed on reboot.pro.

Side effects and alternative uses

Since Windows can see only the first UFD partition without a filter, one can make some Linux files invisible to a Windows user, by storing them on a partition other than the first.

A special case is a pen Linux distro. If you want to use the pen for storing documents too and you don't want in Windows to make Linux OS files visible, simply do not install the Linux on the first partition.

Windows must be able to recognize the flash drive as a "fixed disk."

This is accomplished by either flipping the removable bit (which doesn't always work), or modifying the cfadisk.c, and .inf files, assuming you're on XP. (You must know how to code for the latter.)

I am coming from a linux perspective, so I would just use cfdisk or if you like a gui, gparted.

You could keep a live CD such as Ubuntu handy for doing these sort of things. Just boot from the CD, do what you have to do, reboot to windows. (it's also great as an emergency rescue solution)