Windows 10 - additional partition : can't format, stated as RAW

[VBoxNewbie]

Hello All,
I'm a newbie with VirtualBox. Hope someone can assist me with this.
My configuration
Host: Mac OS X El Capitan 10.11.6
Guest: Windows 10 64-bit
VBox: 5.1.4 with Extension pack and Guest addiotions both installed

I'm trying a add a partition to my Win10. The vdi file or VHD file (I've tested both) has been added to VBox storage settings, It is then detected within Windows 10.
Unfortunately, I cannot format it. Everythime I've tried to format this partition I received an error message saying "This operation has been aborted because the disk is write protected".
I've been trying from Windows Disk Management console or using Diskpart without success.

I don't understand what's the matter. Why is this partititon write protected? Anyone has an idea?

Thanks for your assistance.

[socratis]

First of all, you're not trying to add/format a partition, you're trying to add/format a hard drive. The analogy is you're not trying to paint a room, you're trying to paint the whole house (your 2nd house to be exact).

Where is the second VDI located? Actually, scratch that and post the "recipe" of the VM, the ".vbox" file:

1. Right-click on the VM in the VirtualBox Manager. Select "Show in Finder".
2. ZIP the selected ".vbox" file and attach it in your response.

[VBoxNewbie]

Hello Socratis,

Sorry for mixing the terms in my request. I do know the difference between disk and partition.

Please find attached the log files

I think I finally fixed my issue, though I don't understand why I had it from the beginning.
After going deeply into VirtualBox manual, I've changed the disk status from "Normal" to "Writethrough" using Virtual Media Manager. After that I could format and the disk is no longer write protected.