Enable nested virtualization:
VBoxManage modifyvm pmx --nested-hw-virt on
Create RAW VMDK:

For partition /dev/sda3 (This creates a RAW virtual disk for the whole sda, but only sda3 will be available from the VM)

VBoxManage internalcommands createrawvmdk -filename new-virtualdisk.vmdk -rawdisk /dev/sda -partitions 3