Formatting a removable USB drive with 2 partitions

TL;DR – Starting with Windows 10 Insider Preview Build 14965, you can format any “Removable” USB Flash Drive with more than one partition. Perfect for installation of large (over 4GB) WIM files on UEFI machines!


Hey all, back from a week at the Microsoft MVP summit, a Week in the UK, and a week in Arizona.

A few weeks ago at the Microsoft MVP summit, an engineering manager with the Windows Product group made an offhand comment about formatting a removable USB drive with two partitions. This took several of us by surprise, because historically, this hasn’t been supported widely without converting to a Fixed disk or something.

Mike Terrill (and Mike Niehaus) already beat me to the punch with some posts, but I wanted to share my results. :^)

The Background

Why is this important? Well as I mentioned in another blog post, as more and more people are booting to UEFI, on USB flash drives formatted with Fat32, with WIM images over 4GB in size, that causes a problem because Fat32 can’t hold files over 4GB in size.

Another solution would be to use the Rufus tool to split a USB drive into multiple partitions with a hidden fat32 partition. However, the problem here is that the hidden partition uses a special UEFI app that is not signed, so it won’t work on UEFI machines with Secure Boot enabled.

This has become even more interesting since Windows Server 2016 came out, with a base WIM image for standard Server SKU that is over 4GB in size. Hum…

The Hardware


I tested on several different USB makes using my Windows 10 (version 1607) laptop. Some would allow me to create a 2nd partition on a removable Flash Drive, others would not giving me an error:

DISKPART> create part pri

No usable free extent could be found. It may be that there is insufficient 
free space to create a partition at the specified size and offset. Specify
different size and offset values or don't specify either to create the maximum 
sized partition. It may be that the disk is partitioned using the MBR disk
partitioning format and the disk contains either 4 primary partitions, (no
more partitions may be created), or 3 primary partitions and one extended
partition, (only logical drives may be created).

Mostly the older and/or cheaper drives didn’t work, but most of the newer and/or name brand drives did work.

Finally I narrowed it down to two different models, both my favorites:

Then I tested against three Operating Systems: Windows 10 Version 1607, Windows 10 Preview, and Windwos 7.0 SP1. All using Diskpart to create multiple partitions.

The script

Diskpart.exe –>

sel disk 1
create part pri size=450
format quick fs=fat32
create part pri
format quick fs=ntfs

The Results:

                                 SanDisk           Transcend
Windows 7 SP1 Build 7601           Pass               Fail
Windows 10  Version 1607           Pass               Fail
Windows 10 Preview 14965           Pass               Pass   

I was able to format my SanDisk into multiple partitions using Windows 7 and beyond.

But I was not able to format the Transcend drive into multiple partitions using Windows 7 or Windows 10 Version 1607, but I was able to partition into multiple partitions on the new Windows 10 Insider Preview 14965.

That’s new!

I haven’t done enough testing using the removable flash drives on older machines, to see if the partitions are still visible, but the results look promising for a start.

Update #1 – 11/28/16:

Found out today that the reason that my SanDisk Extreme disk worked on Windows 7 and Windows 10 1607 may be because the removable Flash disk is reported as “Fixed” rather than “Removable” to the OS. Link.

Update #2 – 11/28/16:

I noticed that when taking the “removable” disk formatted with 2 partitions from Windows 10 Preview 14965 over to Windows 10 Version 1607, only the first partition was visible. As a work around I tried moving the main NTFS partition first and the Fat32 partition second.

sel disk 1
create part pri
shrink desired=450
format quick fs=ntfs
create part pri
format quick fs=fat32