Can't create and mount VHD/VHDX files

Hello,

I'm new to Windows 2012R2 Server, but i have a strange thing on the physical one i have. It's a backup server (146Go Raid-1 + 36To raid-6 with deduplication and iSCSI Target installed).

I would like to create a VHDX in order to have a movable drive letter, in case of server migration, backup or so.

I've seen that there is a few possibilities, but none works on my system: i can't create, attach VHDX (or even VHD files), whatever the way used: diskpart, powershell, mmc with drive managment...

Do someone know what I have possibly missed?

Regards,

Patrick