Hello,
I have a little problem.
When I am looking at the number of physical devices, I have 4 devices my intel integrated twice time, and my 970M GTX twice time as well.
But, I should have only one of each…
Thanks 
Some driver installation maybe messed up.
Is this Windows? You should check in registry \HKLM\SOFTWARE\Khronos\Vulkan\Drivers. If there are duplicate rows there, that would be the cause. How it works in other OSes is described in the LoaderAndLayerInterface.md.
If there are duplicates, it “should” be fine to delete them. Or maybe uninstall all drivers first and delete whats left there and then reinstall drivers.
PS On x64 Windows there’s also a WOW6432Node registry tree for x32 on x64 apps.
I am running on archlinux.
when I uninstall vulkan-driver, the number of 4 devices go down to 2 (2 970MGTX), if I reinstall it, it comes back to 4.
But it is not so important, (maybe I could use to multiply by 2 my performances x)).
When I’ll try on window, and if i have the same issue, I’ll look into the registry ^^
Thanks
Linux seems to use these for the purpose:
/usr/share/vulkan/icd.d
/etc/vulkan/icd.d
$HOME/.local/share/vulkan/icd.d