„The heart of the problem is that Hyper-V locks exclusivly the virtualization feature(s) VT-x of the CPU(s), and will not share them with other software.
VirtualBox can be configured to play nice (as much as technically possible) but also require the other hypervisor to do the same.“

Für-die-virtuelle-Maschine-2DROE_2013-konnte-keine-neue-Sitzung-eröffnet-werden-VT-x-is-not-available-VERR_VMX_NO_VMX-E_FAIL-0x80004005.png

Für die virtuelle Maschine 2DROE_2013 konnte keine neue Sitzung eröffnet werden VT-x is not available VERR_VMX_NO_VMX E_FAIL (0x80004005)

 

creditz: noteirak  @ https://forums.virtualbox.org/viewtopic.php?f=6&t=69011

Warning

Do not run other hypervisors (open-source or commercial virtualization products) together with VirtualBox!

While several hypervisors can normally be installed in parallel, do not attempt to run several virtual machines from competing hypervisors at the same time.

VirtualBox cannot track what another hypervisor is currently attempting to do on the same host, and especially if several products attempt to use hardware virtualization features such as VT-x, this can crash the entire host.

Also, within VirtualBox, you can mix software and hardware virtualization when running multiple VMs.

In certain cases a small performance penalty will be unavoidable when mixing VT-x and software virtualization VMs.

We recommend not mixing virtualization modes if maximum performance and low overhead are essential.

This does not apply to AMD-V.

src: https://www.virtualbox.org/manual/ch10.html

So you will have to remove Hyper-V in order to use Virtualbox (can MS and Oracle work together on this? Would be GREAT)

https://serverfault.com/questions/598223/removing-hyper-v-role-from-windows-server-2012-r2

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