specifically, this command run from in a terminal
VBoxManage internalcommands createrawvmdk - filename "/home/catherdersoflinux/Downloads/VirtualBoxStuffs/Artix/windows10sdc.vmdk" -rawdisk /dev/sdc
or atleast that's the version i use for my system. This allows you to use a bare metal install of your other distro (in my case windows 10) inside a virtual box. AND if you're savvy, install a bare metal install of your os from within a virtualbox that you can then boot from outside of virtualbox. I have done both. It was pretty neat. Accessing your bare metal install allows you to update your other os from the comfort of your current os without having to interrupt your work or play. Watch a youtube video while updating your other os, chat with friends on social media without having to switch to a tablet orr phone. send a text or check email. no need to log out or reboot. Very handy.
VBoxManage internalcommands createrawvmdk -filename "/path/where/you/want/the/file/located/YourOsNamePerhaps.vmdk" -rawdisk /dev/sdX
just in case you didn't know...