iometer does not display raw partition

I'm trying to test the performance of my external USB drive. I have two partitions on it. One is formatted as exFAT whereas the other is a RAW windows partition.

I am at a loss about using IOMeter to test the RAW partition. The drive letter never shows up in the disk targets. I see some volume GUIDs in the list so I used DiskExt and this is what I see (my RAW partition is mounted at E:)

D:\Software\DiskExt>diskext.exe

DiskExt v1.2 - Disk extent dumper
Copyright (C) 2001-2016 Mark Russinovich
Sysinternals - www.sysinternals.com

Volume: \\?\Volume{f38b603a-1646-4e9c-b3a8-8a4bad739600}\
   Mounted at: D:\
   Extent [1]:
       Disk:   0
       Offset: 16777216
       Length: 322122547200
Volume: \\?\Volume{72f53ae5-0f2f-414c-83bd-77cbabbfdfad}\
   Mounted at: W:\
   Extent [1]:
       Disk:   0
       Offset: 322139324416
       Length: 177967464448
Volume: \\?\Volume{d02d5e85-24ba-415d-94b8-76829a6c1250}\
   Mounted at: <unmounted>
   Extent [1]:
       Disk:   1
       Offset: 1048576
       Length: 523239424
Volume: \\?\Volume{d672d5ce-8fbc-4a24-9ca0-6d71a76fee6f}\
   Mounted at: C:\
   Extent [1]:
       Disk:   1
       Offset: 645922816
       Length: 1022529208832
Volume: \\?\Volume{29fdf0c8-f4b0-4461-aca1-e4e927eaefcf}\
   Mounted at: <unmounted>
   Extent [1]:
       Disk:   1
       Offset: 1023176343552
       Length: 1032847360
Volume: \\?\Volume{5ad468c4-d836-11e9-9814-f894c28a313e}\
   Mounted at: F:\
   Extent [1]:
       Disk:   2
       Offset: 1048576
       Length: 50790924288
Volume: \\?\Volume{e7d19258-be34-11ed-995d-f894c28a313e}\
   Mounted at: E:\
   Extent [1]:
       Disk:   2
       Offset: 50791972864
       Length: 10737418240
Volume: \\?\Volume{8348666d-21ff-4ae3-b2aa-04271e774e72}\
   Mounted at: <unmounted>
   Extent [1]:
       Disk:   1
       Offset: 524288000
       Length: 104857600

The volume GUID i'm looking at is e7d19258-be34-11ed-995d-f894c28a313e, second from below in the list above. My IOMeter windows shows this:

Has anyone ever used IOMeter with a raw partition? Dynamo seems to have a FORCE_RAW flag but I'm not sure how to use this so that my raw partition shows up in IOMeter. I even tried having all partitions removed hoping it would present itself as a raw disk but iometer still wouldn't see it.

Any pointers?